doc(bloc_helper): update readme

packages/wyatt_bloc_helper/README.md

@@ -116,6 +116,19 @@ Widget onBuild(BuildContext context, CounterState state) {
 }
 ```
 
+If needed, you can wrap what depends on the state with the function `onWrap`.
+
+```dart
+@override
+Widget onWrap(BuildContext context, Widget child) {
+    return Scaffold(
+        appBar: AppBar(
+            title: const Text('Title'),
+        ),
+        body: child,
+    );
+```
+
 > Note: you can override `onBuild`, but also `onListen`, `shouldBuildWhen` and `shouldListenWhen` methods.
 
 ### Both BlocProvider and BlocConsumer