docs: update App component usage (#43030)

components/app/index.en-US.md

@@ -8,11 +8,12 @@ demo:
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-New App Component which provide global style & static function replacement.
+Application wrapper for some global usages.
 
 ## When To Use
 
-Static function in React 18 concurrent mode will not well support. In v5, we recommend to use hooks for the static replacement. But it will make user manual work on define this.
+- Provide reset styles based on `.ant-app` element.
+- You could use static methods of `message/notification/Modal` form `useApp` without put `contextHolder` mannully.
 
 ## Examples