Update links to forum

Author: knolleary

_includes/footer.html

@@ -24,7 +24,7 @@
             <ul>
                 <li><a href="/blog">Blog</a></li>
                 <li><a href="https://twitter.com/nodered">Twitter</a></li>
-                <li><a href="https://groups.google.com/forum/#!forum/node-red">Mailing List</a></li>
+                <li><a href="https://discourse.nodered.org">Forum</a></li>
                 <li><a href="/slack">Slack</a></li>
             </ul>
         </div>

_includes/header.html

@@ -40,6 +40,7 @@
             <li {% if page.url contains '/about/' %}class="current"{% endif %}><a href="/about/">about</a></li>
             <li {% if page.url contains '/blog/' %}class="current"{% endif %}><a href="/blog/">blog</a></li>
             <li {% if page.url contains '/docs/' %}class="current"{% endif %}><a href="/docs/">documentation</a></li>
+            <li><a href="https://discourse.nodered.org/">forum</a></li>
             <li><a href="https://flows.nodered.org/">flows</a></li>
             <li><a href="https://github.com/node-red">github</a></li>
         </ul>

about/community/index.md

@@ -7,9 +7,13 @@ title: Get involved
 
 The two main places to discuss Node-RED are:
 
- - the [mailing list](https://groups.google.com/forum/#!forum/node-red)
+ - the [Node-RED forum](https://discourse.nodered.org)
  - the [slack team](https://nodered.org/slack)
 
+There is also the Google Groups based [mailing list](https://groups.google.com/forum/#!forum/node-red), but
+we are in the process of moving the community over to the new [Node-RED forum](https://discourse.nodered.org).
+The Google Group will become a read-only archive at some point in the near future.
+
 These are the best places to get started if you're stuck on something, think you may
 have hit a bug, have a suggestion for the greatest feature ever or if you just
 want to say hello.

index.html

@@ -140,7 +140,7 @@ <h3>Who's using Node-RED?</h3>
                 <div class="social">
                     <h3>Community <a class="box-link" href="/about/community/">more</a></h3>
                     <ul>
-                        <li><a class="box-link" href="https://groups.google.com/forum/#!forum/node-red"><i class="fa fa-envelope-o fa-3x"></i><br/>Mailing list</a></li>
+                        <li><a class="box-link" href="https://discourse.nodered.org"><i class="fa fa-commenting-o fa-3x"></i><br/>Forum</a></li>
                         <li><a class="box-link" href="/slack"><i class="fa fa-slack fa-3x"></i><br/>Slack team</a></li>
                         <li><a class="box-link" href="https://stackoverflow.com/questions/tagged/node-red"><i class="fa fa-stack-overflow fa-3x"></i><br/>Stack Overflow</a></li>
                         <li><a class="box-link" href="https://github.com/node-red"><i class="fa fa-github fa-3x"></i><br/>GitHub</a></li>