added gitter and mailing list

Author: story645

communications_guidelines.md

@@ -12,8 +12,9 @@ These guidelines are applicable when acting as a representative of Matplotlib (f
     * https://mail.python.org/mailman/listinfo/matplotlib-users
     * https://mail.python.org/mailman/listinfo/matplotlib-devel
 
-## Mailing List:
-social media contributors: [email protected]
+## Social Media Coordination Communication Channels:
+team mailing list: [email protected]
+public chat room: https://gitter.im/matplotlib/community 
 
 ## Content Guidelines:
 - stick to Matplotlib, 3rd party packages, and visualizations made with Matplotlib