List new project in introduction (PyGithub#1739)

Fixes PyGithub#1677

Author: s-t-e-v-e-n-k

doc/introduction.rst

@@ -78,6 +78,7 @@ Projects using PyGithub
 * https://github.com/SOM-Research/Gitana - a SQL-based Project Activity Inspector
 * https://github.com/plus3it/satsuki - Automate GitHub releases and uploading binary release assets
 * `check-in <https://github.com/webknjaz/check-in>`_ — Python CLI distribution that allows user to use GitHub Checks API as a bot.
+* https://github.com/hasii2011/gittodoistclone - Convert GitHub issues to Todoist tasks
 
 They talk about PyGithub
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