Link to matrix rather than IRC

src/report/template.html

@@ -98,7 +98,7 @@ <h3 id="help">How can I help?</h3>
 <ul>
 <li>Look at <a href="https://github.com/NixOS/nixpkgs/issues?q=is%3Aopen+is%3Aissue+label%3A%226.topic%3A+reproducible+builds%22">issues</a> and <a href="https://github.com/NixOS/nixpkgs/pulls?q=is%3Aopen+is%3Apr+label%3A%226.topic%3A+reproducible+builds%22">pull requests</a> with the 'reproducible builds' label.</li>
 <li>Open new issues/PR's for reproducibility problems (like the ones reported above)</li>
-<li>Join the <a href="irc://irc.freenode.net/#nixos-r13y">#nixos-r13y</a> channel on freenode</li>
+<li>Join the <a href="https://matrix.to/#/#reproducible-builds:nixos.org">#reproducible-builds:nixos.org</a> channel on Matrix</li>
 </ul>
 
 <h3 id="next-steps">How can we do better?</h3>