[DOCS] Fix bracket and add tip for page ts configuration

Documentation/Configuration/Index.rst

@@ -63,9 +63,17 @@ Typical example
       basic_auth_password =
       listunsubscribe_enable = 1
       listunsubscribe_email = unsubscribe@example.com
-}
    }
 
+.. tip::
+
+   Configuration is written to the newsletter when it's created. Therefore it's
+   necessary to set all needed values before creating a newsletter.
+   If a newsletter is created already and page ts config changed afterwards,
+   the values of configuration are still the old one in the existing newsletter.
+   You must delete the newsletter and creating a new one to get the new values
+   of the configuration.
+
 Taskqueue
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