message: [Doc] Picker: add demo of usage with popup
diff: @@ -75,6 +75,46 @@ export default {
  };
  ```
  +### With Popup
  +
  +```html
  +<van-field
  + readonly
  + clickable
  + label="City"
  + :value="value"
  + placeholder="Choose City"
  + @click="showPicker = true"
  +/>
  +
  +<van-popup v-model="showPicker" position="bottom">
  + <van-picker
  + show-toolbar
  + :columns="columns"
  + @cancel="showPicker = false"
  + @confirm="onConfirm"
  + />
  +</van-popup>
  +```
  +
  +```js
  +export default {
  + data() {
  + return {
  + value: '',
  + showPicker: false,
  + columns: ['Delaware', 'Florida', 'Georqia', 'Indiana', 'Maine']
  + }
  + },
  + methods: {
  + onConfirm(value) {
  + this.value = value;
  + this.showPicker = false;
  + }
  + }
  +};
  +```
  +
  ### Disable option
  ```html
  