Adding default PHP format

Info is taken from symfony#17515 (comment)

Author: ThomasLandauer

routing.rst

@@ -151,9 +151,8 @@ the ``BlogController``:
 
 .. note::
 
-    By default Symfony only loads the routes defined in YAML format. If you
-    define routes in XML and/or PHP formats, update the ``src/Kernel.php`` file
-    to add support for the ``.xml`` and ``.php`` file extensions.
+    By default Symfony only loads the routes defined in YAML and PHP format. If you
+    define routes in XML, you need to update the ``src/Kernel.php`` file.
 
 .. _routing-matching-http-methods: