DOCSP-12896 add note to --restoreDbUsersAndRoles for admin DB

Author: andf-mongodb

source/reference/program/mongorestore.txt

@@ -752,7 +752,15 @@ Options
    Restore user and role definitions for the given database. See
    :doc:`/reference/system-roles-collection` and
    :doc:`/reference/system-users-collection` for more information.
-   
+
+   .. note::
+
+      The :option:`--restoreDbUsersAndRoles` option cannot be used if
+      specifying the ``admin`` database to the :option:`--db
+      <mongorestore --db>` option, and attempting to do so will result
+      in an error. Restoring the ``admin`` database by specifying
+      :option:`--db admin <mongorestore --db>` to
+      :program:`mongorestore` already restores all users and roles.
 
 
 .. option:: --writeConcern <document>