Merge pull request #13121 from nextcloud/backport/13119/stable30

Author: skjnldsv

admin_manual/configuration_user/user_configuration.rst

@@ -51,8 +51,10 @@ User accounts have the following properties:
 
 *Group Admin*
   Group admins are granted administrative privileges on specific groups, and
-  can add and remove users from their groups. This means they can modify the
-  username, password, email, quota, etc. of members of the group.
+  can create and remove users from their groups. This means they can modify the
+  username, password, email, quota, etc. of members of the group. Group admins
+  are not allowed to add existing users to their groups.
+
 
 *Quota*
   The maximum disk space assigned to each user. Any user that exceeds the quota