docs: update menu developers notes

components/menu/index.en-US.md

@@ -14,6 +14,8 @@ Navigation is an important part of any website, as a good navigation setup allow
 
 More layouts with navigation: [Layout](/components/layout).
 
+## Notes for developers
+
 - Menu render as `ul` element. So it only support [`li` and `script-supporting` elements](https://html.spec.whatwg.org/multipage/grouping-content.html#the-ul-element) as children node。Your customize node should wrapped by `Menu.Item`.
 - Menu need collect node structure. So it's children node should be `Menu.*` or HOC which used by it.
 

components/menu/index.zh-CN.md

@@ -15,6 +15,8 @@ cover: https://gw.alipayobjects.com/zos/alicdn/3XZcjGpvK/Menu.svg
 
 更多布局和导航的使用可以参考：[通用布局](/components/layout)。
 
+## 开发者注意事项
+
 - Menu 元素为 `ul`，因而仅支持 [`li` 以及 `script-supporting` 子元素](https://html.spec.whatwg.org/multipage/grouping-content.html#the-ul-element)。因而你的子节点元素应该都在 `Menu.Item` 内使用。
 - Menu 需要计算节点结构，因而其子元素仅支持 `Menu.*` 以及对此进行封装的 HOC 组件。