message: docs(Picker): update document
diff: @@ -159,7 +159,7 @@ export default {
  };
  ```
  -### Multi columns
  +### Set Column Values
  ```html
  <van-picker :columns="columns" @change="onChange" />
  @@ -175,15 +175,8 @@ export default {
  data() {
  return {
  columns: [
  - {
  - values: Object.keys(states),
  - className: 'column1'
  - },
  - {
  - values: states.Group1,
  - className: 'column2',
  - defaultIndex: 2
  - }
  + { values: Object.keys(states) },
  + { values: states.Group1 }
  ]
  };
  },
  @@ -200,7 +193,24 @@ export default {
  When Picker columns data is acquired asynchronously, use `loading` prop to show loading prompt
  ```html
  -<van-picker :columns="columns" loading />
  +<van-picker :columns="columns" :loading="loading" />
  +```
  +
  +```js
  +export default {
  + data() {
  + return {
  + columns: [],
  + loading: true
  + };
  + },
  + created() {
  + setTimeout(() => {
  + this.loading = false;
  + this.columns = ['Option'];
  + }, 1000);
  + }
  +};
  ```
  ### With Popup
  