Update messenger.rst

Co-Authored-By: Wouter J <[email protected]>

Author: weaverryan

messenger.rst

@@ -301,6 +301,7 @@ to multiple transport:
         $container->loadFromExtension('framework', [
             'messenger' => [
                 'routing' => [
+                    // route all messages that extend this example base class or interface
                     'App\Message\AbstractAsyncMessage' => 'async',
                     'App\Message\AsyncMessageInterface' => 'async',
                     'My\Message\ToBeSentToTwoSenders' => ['async', 'audit'],