message: docs(SubmitBar): use composition api
diff: @@ -18,6 +18,22 @@ app.use(SubmitBar);
  <van-submit-bar :price="3050" button-text="Submit" @submit="onSubmit" />
  ```
  +```js
  +import { Toast } from 'vant';
  +
  +export default {
  + setup() {
  + const onSubmit = () => {
  + Toast('Submit');
  + };
  +
  + return {
  + onSubmit,
  + };
  + },
  +};
  +```
  +
  ### Disabled
  `submit` event will not triggerd when disabled.
  @@ -48,12 +64,30 @@ Use slot to add custom contents.
  ```html
  <van-submit-bar :price="3050" button-text="Submit" @submit="onSubmit">
  <van-checkbox v-model="checked">Check</van-checkbox>
  - <template #tip>
  - Some tips, <span @click="onClickEditAddress">Link</span>
  - </template>
  + <template #tip> Some tips, <span @click="onClickLink">Link</span> </template>
  </van-submit-bar>
  ```
  +```js
  +import { Toast } from 'vant';
  +
  +export default {
  + setup() {
  + const onSubmit = () => {
  + Toast('Submit');
  + };
  + const onClickLink = () => {
  + Toast('Click Link');
  + };
  +
  + return {
  + onSubmit,
  + onClickLink,
  + };
  + },
  +};
  +```
  +
  ## API
  ### Props
  