docs: instruction about antd/es/button

docs/react/getting-started.en-US.md

@@ -188,6 +188,8 @@ import Button from 'antd/lib/button';
 import 'antd/lib/button/style'; // or antd/lib/button/style/css for css format file
 ```
 
+> `antd/es/button` to import es version module for tree shaking.
+
 We strongly recommend using [babel-plugin-import](https://github.com/ant-design/babel-plugin-import), which can convert the following code to the 'antd/lib/xxx' way:
 
 ```jsx

docs/react/getting-started.zh-CN.md

@@ -188,6 +188,8 @@ import Button from 'antd/lib/button';
 import 'antd/lib/button/style'; // 或者 antd/lib/button/style/css 加载 css 文件
 ```
 
+> `antd/es/button` 可以加载 ES 版本的模块，方便进一步 Tree Shake.
+
 如果你使用了 babel，那么可以使用 [babel-plugin-import](https://github.com/ant-design/babel-plugin-import) 来进行按需加载，加入这个插件后。你可以仍然这么写：
 
 ```jsx