[Docs] Added google groups

Resources/doc/index.rst

@@ -1,6 +1,11 @@
 Welcome to SonataUserBundle Documentation
 =========================================
 
+**Google Groups**: For questions and proposals you can post on this google groups
+
+* [Sonata Users](https://groups.google.com/group/sonata-users): Only for user questions
+* [Sonata Devs](https://groups.google.com/group/sonata-devs): Only for devs
+
 Reference Guide
 ---------------