docs(user-manual): add a note about opting out of classification

Signed-off-by: Hamza <[email protected]>

Author: hamza221

user_manual/groupware/mail.rst

@@ -73,6 +73,8 @@ Messages will automatically be marked as important based on which messages you i
 
 .. figure:: images/priority-inbox.png
 
+.. note:: You can opt out of classifying messages as important in account settings, or while adding a new mail account.
+
 All inboxes
 ~~~~~~~~~~~~
 All messages from all the accounts you have logged in, will be shown here chronologically.