docs: add link to Matrix room

Fixes #2639

README.md

@@ -47,8 +47,9 @@ all this out you can go ahead and read the rest of this text.
 Contact
 -------
 
-You can chat with us on IRC in the channel [#home-manager][] on
-[OFTC][].
+You can chat with us on IRC in the channel [#home-manager][] on [OFTC][].
+There is also a [Matrix roome](https://matrix.to/#/#hm:rycee.net),
+which is bridged to the IRC channel.
 
 Installation
 ------------

docs/manual.xml

@@ -16,6 +16,8 @@
    If you encounter problems then please reach out on the IRC channel
    <link xlink:href="https://webchat.oftc.net/?channels=home-manager">#home-manager</link>
    hosted by <link xlink:href="https://oftc.net/">OFTC</link>.
+   There is also a <link xlink:href="https://matrix.to/#/%23hm:rycee.net">Matrix room</link>,
+   which is bridged to the IRC channel.
    If your problem is caused by a bug in Home Manager then it should
    be reported on the
    <link xlink:href="https://github.com/nix-community/home-manager/issues">Home Manager issue tracker</link>.