[Doc] add introduction page (#452)

docs/markdown/en-US/i18n.md

@@ -1,4 +1,4 @@
-# Internationalization
+## Internationalization
 The default language of Vant is Chinese. If you want to use other languages, you can follow the instructions below.
 
 ### Switch languages

docs/markdown/en-US/intro.md

@@ -0,0 +1,38 @@
+<div class="van-doc-intro">
+  <img class="van-doc-intro__youzan" src="//img.yzcdn.cn/public_files/2017/02/09/e84aa8cbbf7852688c86218c1f3bbf17.png">
+  <img class="van-doc-intro__logo" src="//img.yzcdn.cn/public_files/2017/12/18/fd78cf6bb5d12e2a119d0576bedfd230.png">
+  <h2>Vant</h2>
+  <p>A Vue.js 2.0 Mobile UI at YouZan</p>
+</div>
+ 
+### Features
+
+* 48+ Reusable components
+* 90%+ Unit test coverage
+* Extensive documentation and demos
+* Support [babel-plugin-import](https://github.com/ant-design/babel-plugin-import)
+* Support TypeScript
+* Support SSR
+
+### Quickstart
+
+See in [Quickstart](https://www.youzanyun.com/zanui/vant#/en-US/component/quickstart).
+
+### Contribution
+
+Please make sure to read the [Contributing Guide](https://github.com/youzan/vant/blob/dev/.github/CONTRIBUTING.md) before making a pull request.
+
+### Browser Support
+
+Modern browsers and Android 4.0+, iOS 6+.
+
+### Links
+
+* [Changelog](https://www.youzanyun.com/zanui/vant#/en-US/component/changelog)
+* [Weapp UI](https://github.com/youzan/zanui-weapp)
+* [Vant Demo](https://github.com/youzan/vant-demo)
+* [vue-cli-template-vant](https://github.com/youzan/vue-cli-template-vant)
+
+### LICENSE
+
+[MIT](https://zh.wikipedia.org/wiki/MIT%E8%A8%B1%E5%8F%AF%E8%AD%89)