Merge pull request #13735 from nextcloud/backport/13729/stable30

[stable30] feat(20.1): add documentation for talk 20.1

Author: DorraJaouad

user_manual/talk/advanced_features.rst

@@ -239,4 +239,12 @@ By accepting the invite, conversation will appear in the list as any other one.
 .. image:: images/federation-conversations-list.png
    :width: 400px
 
+You can use it further to chat with participants from other federated servers, join calls and use other available Talk features.
+
+Chat summary
+------------
+
+When AI assistant is enabled, a summary can be generated if there are more than 100 unread messages.
+You can generate it by pressing the button that is visible in chat above the first unread messages.
+  
 You can use it further to chat with participants from other federated servers, join calls and use other available Talk features.