Update screenshot and add bot user guide (jenkinsci#648)

Author: timja

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+  "fences": true
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+# Changelog
+
+The CHANGELOG is now maintained on the GitHub releases page:
+<https://github.com/jenkinsci/slack-plugin/releases>
+
+## 2.19 release notes (2019-03-16)
+
+### New features
+
+-   Folder credential support [PR #541](https://github.com/jenkinsci/slack-plugin/pull/541)
+-   Simplify and Groovyfy attachment handling [PR #536](https://github.com/jenkinsci/slack-plugin/pull/536)
+
+## 2.18 release notes (2019-02-19)
+
+### New features
+
+-   Clarify the messaging around the failure notification options [PR #519](https://github.com/jenkinsci/slack-plugin/pull/519)
+-   Add additional logging for notification conditions [PR #516](https://github.com/jenkinsci/slack-plugin/pull/516)
+
+### Internal
+
+-   Introduce maven-checkstyle-plugin to validate no star imports [PR #521](https://github.com/jenkinsci/slack-plugin/pull/521)
+
+## 2.17 release notes (2019-02-13)
+
+### Bug fixes:
+
+-   Fix migration - credentials weren't being saved [PR #513](https://github.com/jenkinsci/slack-plugin/pull/513)
+-   Use correct scope for migrated credential [PR #515](https://github.com/jenkinsci/slack-plugin/pull/515)
+-   Remove 1.8 migration code and SlackJobProperty [PR #514](https://github.com/jenkinsci/slack-plugin/pull/514)
+
+## 2.16 release notes (2019-02-07)
+
+### Bug fixes:
+
+-   java.lang.NumberFormatException: When using parametrized scheduler [PR #510](https://github.com/jenkinsci/slack-plugin/pull/510)
+
+## 2.15 release notes (2019-02-01)
+
+### Removed functionality
+
+-   Integration token text removed from global configuration, it will be automatically migrated into a credential for you. There's upcoming changes for jobs and pipelines in this area as well [PR #493](https://github.com/jenkinsci/slack-plugin/pull/493)
+
+### Bug fixes
+
+-   Add null check to extractReplaceLinks [PR #497](https://github.com/jenkinsci/slack-plugin/pull/497)
+
+### New features
+
+-   Log response string to assist user [PR #486](https://github.com/jenkinsci/slack-plugin/pull/486)
+-   Add class name to failed test notification [PR #474](https://github.com/jenkinsci/slack-plugin/pull/474)
+
+### Internal
+
+-   Remove overriding plugin pom config [PR #492](https://github.com/jenkinsci/slack-plugin/pull/492)
+-   Remove deprecated code [PR #491](https://github.com/jenkinsci/slack-plugin/pull/491)
+-   Bump baseline and parent pom [PR #485](https://github.com/jenkinsci/slack-plugin/pull/485)
+-   IntelliJ automatic code cleanup [PR #484](https://github.com/jenkinsci/slack-plugin/pull/484)
+-   Remove token botUser hack [PR #483](https://github.com/jenkinsci/slack-plugin/pull/483)
+
+## 2.14 release notes
+
+### New features:
+
+-   Allow broadcasting thread messages to the channel [PR #473](https://github.com/jenkinsci/slack-plugin/pull/473)
+
+### Bug fixes:
+
+-   Fix UI fields [PR #471](https://github.com/jenkinsci/slack-plugin/pull/471)
+
+## 2.13 release notes
+
+### Bug fixes:
+
+-   Fixed constructor of SlackJobProperty [PR #468](https://github.com/jenkinsci/slack-plugin/pull/468)
+-   Adding null check on custom message [PR #466](https://github.com/jenkinsci/slack-plugin/pull/466)
+-   Always runAfterFinalized [PR #462](https://github.com/jenkinsci/slack-plugin/pull/462)
+
+### Docs updates:
+
+-   Added note for Global Slack Notifications [PR #470](https://github.com/jenkinsci/slack-plugin/pull/470)
+
+## 2.12 release notes
+
+### Bug fixes:
+
+-   Revert 'Don't publish twice, while the build isn't finished yet' [PR #457](https://github.com/jenkinsci/slack-plugin/pull/457)
+
+## 2.11 release notes
+
+### Bug fixes:
+
+-   Move optional params to setters and fix constructor compatibility [PR #452](https://github.com/jenkinsci/slack-plugin/pull/452)
+
+## 2.10 release notes
+
+### New features:
+
+-   Send only one message with commit list [PR #448](https://github.com/jenkinsci/slack-plugin/pull/448)
+-   Custom messages per Build result [PR #445](https://github.com/jenkinsci/slack-plugin/pull/445)
+
+### Bug fixes:
+
+-   Don't publish twice, while the build isn't finished yet [PR #446](https://github.com/jenkinsci/slack-plugin/pull/446)
+-   Fix compatibility for getBotUser [PR #449](https://github.com/jenkinsci/slack-plugin/pull/449)
+
+## 2.9 release notes
+
+### Bug fixes:
+
+-   Don't hide custom message if var unset [PR #442](https://github.com/jenkinsci/slack-plugin/pull/442)
+-   Rename base url to slack compatible app url [PR #443](https://github.com/jenkinsci/slack-plugin/pull/443)
+
+## 2.8 release notes
+
+### Bug fixes:
+
+-   Make pipeline response object safer [PR #439](https://github.com/jenkinsci/slack-plugin/pull/439)
+
+## 2.7 release notes
+
+### New features:
+
+-   Pipeline response object (threading enhancement) [PR #429](https://github.com/jenkinsci/slack-plugin/pull/429)
+-   Add message when attachments are present [PR #426](https://github.com/jenkinsci/slack-plugin/pull/426)
+
+## 2.6 release notes
+
+### Bug fixes:
+
+-   slack send should not require message [PR #434](https://github.com/jenkinsci/slack-plugin/pull/434)
+
+## 2.5 release notes
+
+### Bug fixes:
+
+-   replace # with nothing in chat.postMessage [PR #433](https://github.com/jenkinsci/slack-plugin/pull/433)
+-   Fix serialisation of some fields [PR #430](https://github.com/jenkinsci/slack-plugin/pull/430)
+
+### Internal updates:
+
+-   Re-enable windows tests on CI [PR #424](https://github.com/jenkinsci/slack-plugin/pull/424)
+
+## 2.4 release notes
+
+### New Features:
+
+-   Support JCasC [PR #404](https://github.com/jenkinsci/slack-plugin/pull/404) [JENKINS-53641](https://issues.jenkins-ci.org/browse/JENKINS-53641)
+    -   [example](/README.md#configuration-as-code)
+-   Add Token Macro support [PR #401](https://github.com/jenkinsci/slack-plugin/pull/401)
+-   Add slash command support [PR #345](https://github.com/jenkinsci/slack-plugin/pull/345)
+-   Add thread support [PR #377](https://github.com/jenkinsci/slack-plugin/pull/377)
+
+### Bug Fixes:
+
+-   [JENKINS-50706] Fix permission check for credentials checkbox [PR #372](https://github.com/jenkinsci/slack-plugin/pull/372)
+-   [JENKINS-37339] Prevent NPE after plugin installation [PR #403](https://github.com/jenkinsci/slack-plugin/pull/403)
+-   [JENKINS-53450] Rename the variable that fails the tests on Windows [PR #394](https://github.com/jenkinsci/slack-plugin/pull/394)
+-   added @DataBoundSetter for includeTestSummary [PR #393](https://github.com/jenkinsci/slack-plugin/pull/393)
+-   Reduce verbosity for standard case when the migrator does nothing [PR #395](https://github.com/jenkinsci/slack-plugin/pull/395)
+-   Create Jenkinsfile [PR #405](https://github.com/jenkinsci/slack-plugin/pull/405)
+-   slack outgoing webhook isn't working [PR #344](https://github.com/jenkinsci/slack-plugin/pull/344)
+-   integration credential logging removed [PR #407](https://github.com/jenkinsci/slack-plugin/pull/407)
+
+### Dependency upgrades:
+
+-   jackson-databind -> 2.8.11.2, [PR #400](https://github.com/jenkinsci/slack-plugin/pull/400)
+
+### Documentation updates:
+
+-   Added multiple channel comment to slackSend [PR #399](https://github.com/jenkinsci/slack-plugin/pull/399)
+-   Send to users wording tweak [PR #408](https://github.com/jenkinsci/slack-plugin/pull/408)
+
+### Internal updates:
+
+-   Parent pom update, new jenkins baseline (2.60.3) and java 8 required  [PR #406](https://github.com/jenkinsci/slack-plugin/pull/406)
+
+## 2.3 release notes
+
+### New Features:
+
+-   Send more advanced slack messages v2 [PR #324](https://github.com/jenkinsci/slack-plugin/pull/324)
+
+### Bug Fixes:
+
+-   Stop log spam [PR #316](https://github.com/jenkinsci/slack-plugin/pull/316)
+
+## 2.2 release notes
+
+### New Features:
+
+-   Implement bot-user support ([#258][#258])
+-   Use DataBoundSetter for optional params ([#236][#236], [#232][#232])
+-   Add `Include failed Tests` ([#166][#166])
+-   Add display failed tests option to slack notifications on job configuration
+    ([#275][#275])
+-   Add baseUrl parameter to support slack-compatible integrations like Mattermost
+    or Rocket Chat ([#293][#293])
+-   Regression notification implemented ([#294][#294])
+
+### Bug Fixes:
+
+-   Fix #126 Replace `<a>` tags with Slack `<link|name>` ([#222][#222],
+    [#126][#126])
+-   Fix #188 Fixes for configuration migration from 1.8 to 2.0 ([#202][#202],
+    [#188][#188])
+-   Changed calculation of `Back to normal` time ([#228][#228], [#225][#225])
+-   Only send `Back to normal` if `Notify Back To Normal` is enabled
+    ([#164][#164])
+-   Add custom message for manually triggered builds on build start ([#162][#162])
+-   Fix #62 by excluding empty affected files collection ([#197][#197],
+    [#62][#62])
+-   Moved message to `text` instead of `fields` to resolve truncated message issue
+    ([#274][#274])
+
+[#126]: https://github.com/jenkinsci/slack-plugin/issues/126
+
+[#162]: https://github.com/jenkinsci/slack-plugin/issues/162
+
+[#164]: https://github.com/jenkinsci/slack-plugin/issues/164
+
+[#166]: https://github.com/jenkinsci/slack-plugin/issues/166
+
+[#188]: https://github.com/jenkinsci/slack-plugin/issues/188
+
+[#197]: https://github.com/jenkinsci/slack-plugin/issues/197
+
+[#202]: https://github.com/jenkinsci/slack-plugin/issues/202
+
+[#222]: https://github.com/jenkinsci/slack-plugin/issues/222
+
+[#225]: https://github.com/jenkinsci/slack-plugin/issues/225
+
+[#228]: https://github.com/jenkinsci/slack-plugin/issues/228
+
+[#232]: https://github.com/jenkinsci/slack-plugin/issues/232
+
+[#236]: https://github.com/jenkinsci/slack-plugin/issues/236
+
+[#258]: https://github.com/jenkinsci/slack-plugin/issues/258
+
+[#274]: https://github.com/jenkinsci/slack-plugin/issues/274
+
+[#275]: https://github.com/jenkinsci/slack-plugin/issues/275
+
+[#293]: https://github.com/jenkinsci/slack-plugin/issues/293
+
+[#294]: https://github.com/jenkinsci/slack-plugin/issues/294
+
+[#62]: https://github.com/jenkinsci/slack-plugin/issues/62
+
+## 2.1 release notes
+
+### New Features:
+
+-   Added Jenkins Credentials support (#247)
+-   Added support for display-url-api; will allow Blue Ocean to change display
+    URLs (#245)
+-   Added support for @here and other @mentions (#241)
+-   Reduced log verbosity (#252)
+-   Updated `@Extension` ordinal value to force earlier migration process (#261)
+
+### UI Improvements:
+
+-   Added credentials selection widget (#247)
+
+### Bug Fixes:
+
+-   Fixes for Security issue [JENKINS-35503][JENKINS-35503] (#247)
+-   Fixed documentation for Pipeline step (#220)
+
+[JENKINS-35503]: https://issues.jenkins-ci.org/browse/JENKINS-35503
+
+## 2.0.1 release notes
+
+Bug Fixes:
+
+-   Set webhook endpoint to random uuid based string if not set (PR # 190)
+-   Upgrading to Slack 2.0 outbound webhooks breaks Jenkins  (#191)
+
+## 2.0 release notes
+
+### New Features:
+
+-   Adding configurable webhook endpoint for exposing jenkins commands with a
+    Slack outgoing-webhook (#160)
+-   Added Jenkins Pipeline support via custom step `slackSend`. (#167)
+
+### UI Improvements:
+
+-   Job level configuration was moved under post-build actions with support for
+    migration from previous versions. (#79, #170)
+-   Use Subdomain instead of Domain (#168)
+
+### Bug Fixes
+
+-   Notify for repeated failures doesn't work (#136)
+-   Workflow plugin integration (#50)
+-   "Back to normal" message duration is build duration rather than time the job
+    has been broken for (#129)
+-   [FIXED JENKINS-30559] Dropdown list to select commit info for notifications
+    (#133)
+-   Fix double start message when build is manually started (#96, #137)
+-   "success" instead of "back to normal" after aborted build (123)
+-   Doesn't support the Jenkins Inheritance plugin (#6)
+
+## 1.8.1 release notes
+
+This is a backport release which backports features originally intended for
+slack-2.0 release.  This is meant as a nice fix for people missing critical
+bugs.  Thanks [@Nooba](https://github.com/Nooba/) for taking the time to
+backport all of the changes.  Since new features listed here will also be
+included in the slack-2.0 release I'm not going to bother mentioning them in the
+slack-2.0 release at all.
+
+### New Features:
+
+-   Allow simple markup formatting in custom messages. (#127)
+
+### UI Improvements:
+
+-   Improves custom message help text. (#97)
+
+### Bug fixes:
+
+-   Allow parallel builds. (#122)
+-   Use textarea for customMessage.  This allows custom messages to have new
+    lines. (#103)
+-   Set test connection message color correctly. (#101)
+-   Fix publish to multiple rooms. Add unit tests. (#98, #100)
+-   Include custom message when changes are found. (#95)
+
+## 1.8.0 release notes
+
+### New Features:
+
+-   Option to add a custom message (#49, #78)
+-   Build Server URL defaults to Jenkins URL when the slack plugin is first
+    configured (#42, #90)
+
+### UI Improvements:
+
+-   Move `Test Connection` button in slack job config to the advanced section
+    (#64)
+-   Improvements to `Test Connection` button.  It now provides feedback in the
+    Jenkins UI when it succeeds or fails to connect to the slack instance (#51,
+    \#81)
+
+### Improvements:
+
+-   Improve 'started' message with proper cause (#37)
+-   The separator for specifying posting to multiple slack channels is more
+    robust.  It now allows spaces, commas, and semicolons as a separator (#56)
+-   Notifications start with full project name when using Cloudbees folders
+    plugin.  This includes the folder and the project in the notification (#61)
+-   Search upstream causes when gathering commit list (#67)
+-   Change repeated failure message improvement with `Still Failing`.  Makes it
+    easier to understand if it is the first or repeated failure in a build (#77)
+-   Add unit tests for `doTestConnection` method (#82, #84)
+
+### Bug fixes:
+
+-   Fix `Include Test Summary` and `Notify Repeated Failure` options being
+    reversed when saving settings in the UI (#63)
+-   Change `.getPreviousBuild()` to allow for higher concurrency (#70)
+-   Solve `java.lang.NoClassDefFoundError` when running unit tests (#82, #83)
+-   Adding ability for environment variables and parameters (#31, #80, #89)
+
+## 1.7.0 release notes
+
+### New features:
+
+-   Advanced settings
+    -   Team domain and token can be specified per project; falls back to global
+        config if not specified (#19)
+    -   Post a list of commits with the build notification (title and author of
+        commit) (#30, #44, #45)
+    -   Include JUnit test summary in build notifications (#25)
+-   Use colors when sending a message using slack (#20, #24).  Also, the start
+    notifications use the color of the last build result (#43)
+-   Support for authenticated proxies (#14)
+-   Test Connection button (#46, #28)
+-   Option to disable subsequent notifications on build failures (#46, #15)
+
+### Improvements:
+
+-   Report 'return to normal' on transition from unstable to success (#21).
+-   Improved logging.
+
+### Bug fixes:
+
+-   When changing the global slack settings the slack config in jobs are updated
+    as well (#26, #12)
+-   Fix NullPointerException and output log message if slack is not configured
+    (#35, JENKINS-26066)