Mention Slack in readme

README.rst

@@ -64,7 +64,7 @@ Community Support
 ~~~~~~~~~~~~~~~~~
 There is an active community of Wagtail users and developers responding to questions on `Stack Overflow <http://stackoverflow.com/questions/tagged/wagtail>`_. When posting questions, please read Stack Overflow's advice on `how to ask questions <http://stackoverflow.com/help/how-to-ask>`_ and remember to tag your question with "wagtail".
 
-For topics and discussions that do not fit Stack Overflow's question-and-answer format, there is also a `Wagtail Support mailing list <https://groups.google.com/forum/#!forum/wagtail>`_.
+For topics and discussions that do not fit Stack Overflow's question-and-answer format, there is also a `Wagtail Support mailing list <https://groups.google.com/forum/#!forum/wagtail>`_ and a `Slack workspace <https://github.com/wagtail/wagtail/wiki/Slack>`_.
 
 Commercial Support
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