Added Gitter references [ci skip]

Author: radarhere

.github/CONTRIBUTING.md

@@ -4,7 +4,7 @@ Bug fixes, feature additions, tests, documentation and more can be contributed v
 
 ## Bug fixes, feature additions, etc.
 
-Please send a pull request to the master branch. Please include [documentation](https://pillow.readthedocs.io) and [tests](../Tests/README.rst) for new features. Tests or documentation without bug fixes or feature additions are welcome too. Feel free to ask questions [via issues](https://github.com/python-pillow/Pillow/issues/new) or irc://irc.freenode.net#pil
+Please send a pull request to the master branch. Please include [documentation](https://pillow.readthedocs.io) and [tests](../Tests/README.rst) for new features. Tests or documentation without bug fixes or feature additions are welcome too. Feel free to ask questions [via issues](https://github.com/python-pillow/Pillow/issues/new), [Gitter](https://gitter.im/python-pillow/Pillow) or irc://irc.freenode.net#pil
 
 - Fork the Pillow repository.
 - Create a branch from master.

docs/_templates/sidebarhelp.html

@@ -1,4 +1,4 @@
 <h3>Need help?</h3>
 <p>
-    You can get help via IRC at <a href="irc://irc.freenode.net#pil">irc://irc.freenode.net#pil</a> or Stack Overflow <a href="https://stackoverflow.com/questions/tagged/pillow">here</a> and <a href="https://stackoverflow.com/questions/tagged/python-imaging-library">here</a>. Please <a href="https://github.com/python-pillow/Pillow/issues/new">report issues on GitHub</a>.
+    You can get help via IRC at <a href="irc://irc.freenode.net#pil">irc://irc.freenode.net#pil</a>, <a href="https://gitter.im/python-pillow/Pillow">Gitter</a> or Stack Overflow <a href="https://stackoverflow.com/questions/tagged/pillow">here</a> and <a href="https://stackoverflow.com/questions/tagged/python-imaging-library">here</a>. Please <a href="https://github.com/python-pillow/Pillow/issues/new">report issues on GitHub</a>.
 </p>