Embedding mailing list for RTD. [skip ci]

doc/index.rst

@@ -35,6 +35,19 @@ If you like gevent, :doc:`donate <sfc>` to support the development.
    <a class="twitter-timeline" data-dnt="true" href="https://twitter.com/search?q=gevent" data-widget-id="621692925999644672">Tweets about gevent</a> <script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+"://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs");</script>
 
 
+   <iframe id="forum_embed"
+         src="javascript:void(0)"
+         scrolling="no"
+         frameborder="0"
+         width="900"
+         height="700">
+   </iframe>
+
+   <script type="text/javascript">
+         document.getElementById("forum_embed").src = "https://groups.google.com/forum/embed/?place=forum/gevent"
+             + "&showsearch=true&&showpopout=true&parenturl=" + encodeURIComponent(window.location.href);
+   </script>
+
 .. _coroutine: https://en.wikipedia.org/wiki/Coroutine
 .. _Python: http://python.org
 .. _greenlet: http://greenlet.readthedocs.org