minor symfony#6734 Add little caution to add service id for @route annotation (DHager, WouterJ)

This PR was merged into the 2.7 branch.

Discussion
----------

Add little caution to add service id for @route annotation

Finishes symfony#6258

Original PR description:

 > I just ran into this problem and it took me a while. Without the `@Route(service="myid")` annotation, the controller was *always* being instantiated without any arguments, completely ignoring my service-definition.

 > Not sure how far back/forward this applies to other versions.

Commits
-------

93bb21c Merge caution with annotations tip
ac6b008 Add warning about a pitfall where the controller seems to be instantiated without using the service-definition

Author: wouterj

cookbook/controller/service.rst

@@ -119,7 +119,8 @@ the route ``_controller`` value:
 .. tip::
 
     You can also use annotations to configure routing using a controller
-    defined as a service. See the `FrameworkExtraBundle documentation`_ for
+    defined as a service. Make sure you specify the service ID in the
+    ``@Route`` annotation. See the `FrameworkExtraBundle documentation`_ for
     details.
 
 .. tip::
@@ -338,4 +339,4 @@ controller:
 
 .. _`Controller class source code`: https://github.com/symfony/symfony/blob/master/src/Symfony/Bundle/FrameworkBundle/Controller/Controller.php
 .. _`base Controller class`: https://github.com/symfony/symfony/blob/master/src/Symfony/Bundle/FrameworkBundle/Controller/Controller.php
-.. _`FrameworkExtraBundle documentation`: https://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/annotations/routing.html
+.. _`FrameworkExtraBundle documentation`: https://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/annotations/routing.html#controller-as-service