docs/templates/topindex.html: Update forum link.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

docs/templates/topindex.html

@@ -119,7 +119,7 @@
         <span class="linkdescr">the official MicroPython site</span>
       </p>
       <p class="biglink">
-        <a class="biglink" href="http://forum.micropython.org">MicroPython forum</a><br/>
+        <a class="biglink" href="https://github.com/orgs/micropython/discussions">GitHub Discussions</a><br/>
         <span class="linkdescr">community discussion for all things related to MicroPython</span>
       </p>
     </td>