Update server-data.rst

Author: 94noni

frontend/encore/server-data.rst

@@ -8,7 +8,10 @@ them later in JavaScript. For example:
 
 .. code-block:: html+twig
 
-    <div class="js-user-rating" data-is-authenticated="{{ app.user ? 'true' : 'false' }}">
+    <div class="js-user-rating"
+        data-is-authenticated="{{ app.user ? 'true' : 'false' }}"
+        data-user="{{ app.user|serialize(format = 'json') }}"
+    >
         <!-- ... -->
     </div>