message: docs(Sidebar): add change event demo
diff: @@ -52,6 +52,31 @@ export default {
  </van-sidebar>
  ```
  +### Change Event
  +
  +```html
  +<van-sidebar v-model="activeKey" @change="onChange">
  + <van-sidebar-item title="Title1" />
  + <van-sidebar-item title="Title2" />
  + <van-sidebar-item title="Title3" />
  +</van-sidebar>
  +```
  +
  +```js
  +export default {
  + data() {
  + return {
  + activeKey: 0
  + };
  + },
  + methods: {
  + onChange(index) {
  + Notify({ type: 'primary', message: index });
  + }
  + }
  +}
  +```
  +
  ## API
  ### Sidebar Props
  