Clarify ways of communication

We use GitHub issues for some feature request already, it makes sense to
make it our official feature request tracker. Discussion about what and
how to implement go there.

Gitter is used for informal chatting.

Fixes #368.

CONTRIBUTING.md

@@ -28,11 +28,13 @@ Other changes that are cosmetic in nature and do not add anything substantial to
 
 #### **Do you intend to add a new feature or change an existing one?**
 
-* Make sure you discussed this with the relevant people and got some feedback, before you start writing code.
-
+* Please open an [issue](https://github.com/openSUSE/software-o-o/issues/new) to discuss your change before writing any code.
 * If the changes are visual, consider attaching screenshots showing the before/after change in the Github pull request description.
 
-* Do not open an issue on GitHub until you have collected positive feedback about the change. GitHub issues are primarily intended for bug reports and fixes.
+#### **Do you want to talk to us?**
+
+* We hang out in our [gitter chatroom](https://gitter.im/openSUSE/software-o-o). This is an **informal** chat, please
+  keep discussions about bugs and features on GitHub.
 
 Thanks! :green_heart: :green_heart: :green_heart: