added a Twig example for the service

doc/providers/url_generator.rst

@@ -47,3 +47,19 @@ The UrlGenerator provider provides a ``url_generator`` service::
                ' | '.
                '<a href="'.$app['url_generator']->generate('hello', array('name' => 'Igor')).'">Hello Igor</a>';
     });
+
+
+When using Twig, the service can be used like this::
+
+.. code-block:: jinja
+
+    {{ app.url_generator.generate('homepage') }}
+
+Moreover, if you register the ``SymfonyBridgesServiceProvider``, then you will have access to the native Twig helpers: ``path()`` and ``url()``::
+
+.. code-block:: jinja
+
+    {{ path('homepage') }}
+    {{ url('homepage') }} {# generates the absolute url http://example.org/ #}
+
+You can find more information about this subject in the :doc:`Symfony bridges documentation<symfony_bridges>`.
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