Update the IRC link to point to Libera

Now that we've moved from Freenode

Author: gammafunk

site/index.htm

@@ -45,7 +45,7 @@ <h2>Help & Community</h2>
                 </li>
                 <li><a href="http://crawl.chaosforge.org/">Community Wiki</a>: Game information organized into articles, with a focus on describing the <a href="http://crawl.chaosforge.org/Current_release">stable release</a></li>
                 <li><a href="https://crawl.develz.org/tavern/">Forum</a>: Debate strategy and propose changes on our forums</a></li>
-                <li><a href="http://webchat.freenode.net/?channels=%23%23crawl">IRC</a>: ##crawl on Freenode is filled with helpful souls offering real-time advice</li>
+                <li><a href="https://web.libera.chat/">IRC</a>: #crawl on Libera is filled with helpful souls offering real-time advice</li>
                 <li><a href="https://crawl.develz.org/mantis/">Bug Reports</a>: Found a problem? Let us know!</li>
             </ul>