DOC Document campaign admin filter functionality (#844)

Author: GuySartorelli

en/08_Changelogs/6.2.0.md

@@ -10,6 +10,7 @@ title: 6.2.0 (unreleased)
   - [Accessibility improvements](#accessibility-improvements)
   - [Pass arbitrary attributes with requirements API](#requirements-attributes)
   - [Filter archived records](#filter-archived-records)
+  - [Filter campaigns](#filter-campaigns)
   - [Other new features and enhancements](#other-new)
 - [API changes](#api-changes)
 - [Bug fixes](#bug-fixes)
@@ -104,6 +105,12 @@ The "Archive" admin section now uses [`GridFieldFilterHeader`](api:SilverStripe\
 
 To facilitate this functionality, we've added a way to add extra searchable field configuration to a `SearchContext` instance through [`SearchContext::addAdditionalFieldSpecs()`](api:SilverStripe\ORM\Search\SearchContext::addAdditionalFieldSpecs()) and [`SearchContext::setAdditionalFieldSpecs()`](api:SilverStripe\ORM\Search\SearchContext::setAdditionalFieldSpecs()). If you implement a custom `SearchContext` subclass, you should use [`SearchContext::getSearchFieldsSpec()`](api:SilverStripe\ORM\Search\SearchContext::getSearchFieldsSpec()) instead of directly calling [`searchableFields()`](api:SilverStripe\ORM\DataObject::searchableFields()).
 
+### Filter campaigns
+
+The "Campaigns" admin section which is added through [`silverstripe/campaign-admin`](https://github.com/silverstripe/silverstripe-campaign-admin/) now uses [`GridFieldFilterHeader`](api:SilverStripe\Forms\GridField\GridFieldFilterHeader) and [`SearchContext`](api:SilverStripe\ORM\Search\SearchContext) to allow filtering campaigns.
+
+You can filter by the name and description of the campaign, its status, and the publish date. This is all powered by [`searchable_fields`](/developer_guides/model/scaffolding/#searchable-fields) configuration for the [`ChangeSet`](api:SilverStripe\Versioned\ChangeSet) class, so you can customise the search fields by changing that configuration if you want to.
+
 ### Other new features and enhancements {#other-new}
 
 - The `help` plugin is now added by default to all [`TinyMCEConfig`](api:SilverStripe\TinyMCE\TinyMCEConfig) instances. If you were adding it manually, you can remove that custom code. If for some reason you don't want that plugin in one of your configs, you can use [`TinyMCEConfig::disablePlugins()`](api:SilverStripe\TinyMCE\TinyMCEConfig::disablePlugins()) to remove it - but be aware that it is extremely useful for screen reader users to keep this plugin installed.