Update mailing list references to new forum

.github/ISSUE_TEMPLATE.md

@@ -8,7 +8,9 @@ If your issue is:
  - a feature request or suggestion for a change,
  - or problems with 3rd party (`node-red-contrib-`) nodes
 
-please use the [mailing list](https://groups.google.com/forum/#!forum/node-red), [slack team](https://nodered.org/slack) or ask a question on [Stack Overflow](https://stackoverflow.com/questions/tagged/node-red) and tag it `node-red`.
+please use the [Node-RED Forum](https://discourse.nodered.org) or [slack team](https://nodered.org/slack).
+
+You could also consider asking a question on [Stack Overflow](https://stackoverflow.com/questions/tagged/node-red) and tag it `node-red`.
 
 That way the whole Node-RED user community can help, rather than rely on the core development team.
 

.github/PULL_REQUEST_TEMPLATE.md

@@ -16,7 +16,7 @@ Put an `x` in the boxes that apply
 <!--
 If you want to raise a pull-request with a new feature, or a refactoring
 of existing code, it **may well get rejected** if it hasn't been discussed on
-the [mailing list](https://groups.google.com/forum/#!forum/node-red) or
+the [forum](https://discourse.nodered.org) or
 [slack team](https://nodered.org/slack) first.
 
 -->

CONTRIBUTING.md

@@ -30,13 +30,13 @@ At a minimum, please include:
 
 ## Feature requests
 
-For feature requests, please raise them on the [mailing list](https://groups.google.com/forum/#!forum/node-red).
+For feature requests, please raise them on the [forum](https://discourse.nodered.org).
 
 ## Pull-Requests
 
 If you want to raise a pull-request with a new feature, or a refactoring
 of existing code, it may well get rejected if you haven't discussed it on
-the [mailing list](https://groups.google.com/forum/#!forum/node-red) first.
+the [forum](https://discourse.nodered.org) first.
 
 All contributors need to sign the JS Foundation's Contributor License Agreement.
 It is an online process and quick to do. You can read the details of the agreement

README.md

@@ -22,8 +22,7 @@ started.
 
 More documentation can be found [here](https://nodered.org/docs).
 
-For further help, or general discussion, please use the
-[mailing list](https://groups.google.com/forum/#!forum/node-red).
+For further help, or general discussion, please use the [Node-RED Forum](https://discourse.nodered.org) or [slack team](https://nodered.org/slack).
 
 ## Developers