added upgrade note

Controller/WebsiteArticleController.php

@@ -45,6 +45,7 @@ public function indexAction(Request $request, ArticleInterface $object, $view, $
      * @param ArticleInterface $object
      * @param string $view
      * @param int $pageNumber
+     * @param array $attributes
      *
      * @return Response
      */

UPGRADE.md

@@ -2,6 +2,48 @@
 
 ## dev-develop
 
+### WebsiteArticleController
+
+The multi-page feature needs a refactoring of the ``WebsiteArticleController``.
+If you have overwritten it you have to adapt it.
+
+__Before:__
+
+```php
+class CustomArticleController extends Controller
+{
+    public function indexAction(Request $request, ArticleDocument $object, $view)
+    {
+        $content = $this->get('jms_serializer')->serialize(
+            $object,
+            'array',
+            SerializationContext::create()
+                ->setSerializeNull(true)
+                ->setGroups(['website', 'content'])
+                ->setAttribute('website', true)
+        );
+
+        return $this->render(
+            $view . '.html.twig',
+            $this->get('sulu_website.resolver.template_attribute')->resolve($content),
+            $this->createResponse($request)
+        );
+    }
+}
+```
+
+__After:__
+
+```php
+class CustomArticleController extends WebsiteArticleController
+{
+    public function indexAction(Request $request, ArticleInterface $object, $view, $pageNumber = 1)
+    {
+        return $this->renderArticle($request, $object, $view, $pageNumber, []);
+    }
+}
+```
+
 ### Cachelifetime request attribute changed
 
 The `_cacheLifetime` attribute available in the request parameter of a article