add note about the #composer-dev irc channel to the composer page

src/Packagist/WebBundle/Resources/views/About/aboutComposer.html.twig

@@ -33,4 +33,7 @@
     }
 }
 </pre></p>
+
+    <h1>Community</h1>
+    <p>If you have questions about composer or want to help out, come and join us in the <em>#composer-dev</em> channel on irc.freenode.net.</p>
 {% endblock %}