[Doc] add some english documents (#220)

* [bugfix] Checkbox border render error in weixin browser

* [bugfix] TreeSelect dependency path error

* [bugfix] Swipe should clear autoplay timer when destroyed

docs/examples-docs/en-US/loading.md

@@ -0,0 +1,35 @@
+## Loading
+
+### Install
+``` javascript
+import { Loading } from 'vant';
+
+Vue.component(Loading.name, Loading);
+```
+
+### Usage
+
+#### Solid color
+
+:::demo Solid color
+```html
+<van-loading type="circle" color="black"></van-loading>
+<van-loading type="circle" color="white"></van-loading>
+```
+:::
+
+#### Gradient color
+
+:::demo Gradient color
+```html
+<van-loading type="gradient-circle" color="black"></van-loading>
+<van-loading type="gradient-circle" color="white"></van-loading>
+```
+:::
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| color | Color | `String` | `black` | `black` `white` |
+| type | Type | `String` | `gradient-circle` | `gradient-circle` `circle` |