Bug 1618874 - Add Matrix to Community Page. r=me

src/community.en.html

@@ -86,9 +86,10 @@ SeaMonkey with the ChatZilla IRC Client installed, which you should have with
 a full installation.)
 <p>
 </p>
-We are still monitoring the <a href="irc://irc.mozilla.org/seamonkey">
-#seamonkey channel on irc.mozilla.org</a> until the server will be shut down
-early in 2020.
+There is also the <a href="https://chat.mozilla.org/#/room/#seamonkey:mozilla.org">SeaMonkey room on Matrix</a> which bridges through to the
+<a href="irc://freenode/SeaMonkey">#seamonkey channel on freenode.net</a>.
+For more information on Matrix and other rooms on it, look on the
+<a href="https://wiki.mozilla.org/Matrix">Mozilla Wiki</a>.
 </p>
 
 <h2 id="blogs">Weblogs</h2>