Add the missing note on how to inject a service into the controller

Author: wkania

controller.rst

@@ -178,7 +178,8 @@ These are used for rendering templates, sending emails, querying the database an
 any other "work" you can think of.
 
 If you need a service in a controller, type-hint an argument with its class
-(or interface) name. Symfony will automatically pass you the service you need::
+(or interface) name. Symfony will automatically pass you the service you need.
+Make sure your :doc:`controller is registered as a service </controller/service>`::
 
     use Psr\Log\LoggerInterface;
     use Symfony\Component\HttpFoundation\Response;