Include matrix channel name in link. (#2908)

README.md

@@ -2,7 +2,7 @@
 
 The goal of the Firefox Reality project is to create a full-featured browser exclusively for *standalone* AR and VR headsets.
 
-You can find us on the [Matrix](https://chat.mozilla.org/#/room/#fxr:mozilla.org) ([Instructions for joining](https://wiki.mozilla.org/Matrix)), Twitter [@MozillaReality](https://twitter.com/mozillareality), and at [mixedreality@mozilla.com](mailto:mixedreality@mozilla.com).
+You can find us in [#fxr:mozilla.org on the Matrix](https://chat.mozilla.org/#/room/#fxr:mozilla.org) ([Instructions for joining](https://wiki.mozilla.org/Matrix)), Twitter [@MozillaReality](https://twitter.com/mozillareality), and at [mixedreality@mozilla.com](mailto:mixedreality@mozilla.com).
 
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