minor #7902 Update best_practices/templates.rst (GuilhemN)

This PR was merged into the master branch.

Discussion
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Update best_practices/templates.rst

First example of a doc asserting we're using the 3.3 SE (#7877 (comment)).

Commits
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8769a30 Update best_practices/templates.rst

Author: weaverryan

best_practices/templates.rst

@@ -60,8 +60,8 @@ Twig Extensions
 
 .. best-practice::
 
-    Define your Twig extensions in the ``AppBundle/Twig/`` directory and
-    configure them using the ``app/config/services.yml`` file.
+    Define your Twig extensions in the ``AppBundle/Twig/`` directory. Your
+    application will automatically detect them and configure them.
 
 Our application needs a custom ``md2html`` Twig filter so that we can transform
 the Markdown contents of each post into HTML.
@@ -73,18 +73,8 @@ a new dependency of the project:
 
     $ composer require erusev/parsedown
 
-Then, create a new ``Markdown`` service that will be used later by the Twig
-extension. The service definition only requires the path to the class:
-
-.. code-block:: yaml
-
-    # app/config/services.yml
-    services:
-        # ...
-        app.markdown:
-            class: AppBundle\Utils\Markdown
-
-And the ``Markdown`` class just needs to define one single method to transform
+Then, create a new ``Markdown`` class that will be used later by the Twig
+extension. It just needs to define one single method to transform
 Markdown content into HTML::
 
     namespace AppBundle\Utils;
@@ -107,8 +97,8 @@ Markdown content into HTML::
     }
 
 Next, create a new Twig extension and define a new filter called ``md2html``
-using the ``Twig_SimpleFilter`` class. Inject the newly defined ``markdown``
-service in the constructor of the Twig extension:
+using the ``Twig_SimpleFilter`` class. Inject the newly defined ``Markdown``
+class in the constructor of the Twig extension:
 
 .. code-block:: php
 
@@ -147,18 +137,11 @@ service in the constructor of the Twig extension:
         }
     }
 
-Lastly define a new service to enable this Twig extension in the app (the service
-name is irrelevant because you never use it in your own code):
-
-.. code-block:: yaml
+And that's it!
 
-    # app/config/services.yml
-    services:
-        app.twig.app_extension:
-            class:     AppBundle\Twig\AppExtension
-            arguments: ['@app.markdown']
-            public:    false
-            tags: [twig.extension]
+Your application will :ref:`autoconfigure <services-autoconfigure>` your twig
+extension and inject a ``Markdown`` instance in it thanks to
+:doc:`autowiring </service_container/autowiring>`.
 
 .. _`Twig`: http://twig.sensiolabs.org/
 .. _`Parsedown`: http://parsedown.org/