Update security.rst

Added info about route.

Author: ThomasLandauer

reference/configuration/security.rst

@@ -531,9 +531,9 @@ required by the :class:`Symfony\\Component\\Security\\Core\\User\\UserInterface`
 ``path``
 ~~~~~~~~
 
-**type**: ``string`` **default**: ``/``
+**type**: ``string`` **default**: none
 
-The path which triggers logout.
+The path which triggers logout. You need to configure a route with the same path.
 
 ``success_handler``
 ~~~~~~~~~~~~~~~~~~~