chore: move vant to packages folder (#9384)

packages/vant/docs/markdown/vant-use-intro.en-US.md

@@ -0,0 +1,24 @@
+# Composables
+
+### Intro
+
+Vant provide some built-in composition APIs, you can directly use these APIs for development.
+
+### Demo
+
+```js
+import { useWindowSize } from '@vant/use';
+
+const { width, height } = useWindowSize();
+
+console.log(width.value); // -> window width
+console.log(height.value); // -> window height
+```
+
+### API List
+
+| Name | Description |
+| --- | --- |
+| [useClickAway](#/en-US/use-click-away) | Triggers a callback when user clicks outside of the target element |
+| [useCountDown](#/en-US/use-count-down) | Used to manage the countdown |
+| [useToggle](#/en-US/use-toggle) | Used to switch between `true` and `false` |