minor symfony#10201 [Routing] Update routing.rst, add example routes as annotations (andreybolonin, weaverryan)

This PR was submitted for the 4.1 branch but it was merged into the 4.3 branch instead (closes symfony#10201).

Discussion
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[Routing] Update routing.rst, add example routes as annotations

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Commits
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54743d6 cleaning up some use statements, etc
0a1badf Update routing.rst

Author: javiereguiluz

components/routing.rst

@@ -250,8 +250,22 @@ Annotation Routing Loaders
 Last but not least there are
 :class:`Symfony\\Component\\Routing\\Loader\\AnnotationDirectoryLoader` and
 :class:`Symfony\\Component\\Routing\\Loader\\AnnotationFileLoader` to load
-route definitions from class annotations. The specific details are left
-out here.
+route definitions from class annotations::
+
+    use Doctrine\Common\Annotations\AnnotationReader;
+    use Symfony\Component\Config\FileLocator;
+    use Symfony\Bundle\FrameworkBundle\Routing\AnnotatedRouteControllerLoader;
+    use Symfony\Component\Routing\Loader\AnnotationDirectoryLoader;
+
+    $loader = new AnnotationDirectoryLoader(
+        new FileLocator(__DIR__.'/app/controllers/'),
+        new AnnotatedRouteControllerLoader(
+            new AnnotationReader()
+        )
+    );
+
+    $routes = $loader->load(__DIR__.'/app/controllers/');
+    // ...
 
 .. include:: /_includes/_annotation_loader_tip.rst.inc