[Support] Add link to riot.

support.md

 ---
 layout: page
-title: Github
+title: Support
 category: Support
 ---
 
-Most of the interaction with the development team is done through the github pages of each repository.
+## Github
+Most of the interaction with the development team is done through the [github pages of each repository](https://github.com/stack-of-tasks).
 
+## Chat
+You can also ask directly questions [through matrix](https://riot.laas.fr/#/room/!XoWvdoZDrzoOvUPwag:laas.fr).
+
+## Mailing list
 If you have any problems with the robotpkg binaries you can ask a question to
 [the mailing liste of robotpkg](https://sympa.laas.fr/sympa/info/robotpkg)