Improve explanation

Author: javiereguiluz

security/user_checkers.rst

@@ -37,7 +37,8 @@ or :class:`Symfony\\Component\\Security\\Core\\Exception\\AuthenticationExceptio
             }
 
             if ($user->isDeleted()) {
-                throw new CustomUserMessageAccountStatusException('The user account was not found.');
+                // the message passed to this exception is meant to be displayed to the user
+                throw new CustomUserMessageAccountStatusException('Your user account no longer exists.');
             }
         }