[Docs] fix the format

Resources/doc/index.rst

@@ -3,8 +3,8 @@ 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
+* `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
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