Add documentation for extending IsGranted attribute

Author: tcoch

security.rst

@@ -2523,6 +2523,28 @@ that is thrown with the ``exceptionCode`` argument::
         // ...
     }
 
+Extending ``IsGranted``
+.......................
+
+You can also extend the ``IsGranted`` class to create new attributes:
+
+    // src/Security/Attribute/IsAdmin.php
+    // ...
+
+    use Symfony\Component\Security\Http\Attribute\IsGranted;
+
+    class IsAdmin extends IsGranted
+    {
+        public function __construct() {
+            return parent::__construct('ROLE_ADMIN');
+        }
+    }
+
+    .. versionadded:: 7.4
+
+            The :class:`Symfony\\Component\\Security\\Http\\Attribute\\IsGranted`
+            attribute is extendable since Symfony 7.4.
+
 .. _security-template:
 
 Access Control in Templates