[Doc] SwipeCell: update demo (#3765)

src/swipe-cell/README.zh-CN.md

@@ -16,53 +16,41 @@ Vue.use(SwipeCell);
 
 ```html
 <van-swipe-cell>
-  <van-button
-    square
-    slot="left"
-    type="danger"
-    text="选择"
-  />
-  <van-cell
-    :border="false"
-    title="单元格"
-    value="内容"
-  />
-  <van-button
-    square
-    slot="right"
-    type="danger"
-    text="删除"
-  />
+  <template slot="left">
+    <van-button square type="primary" text="选择" />
+  </template>
+
+  <van-cell :border="false" title="单元格" value="内容" />
+
+  <template slot="right">
+    <van-button square type="danger" text="删除" />
+    <van-button square type="primary" text="收藏"/>
+  </template>
 </van-swipe-cell>
 ```
 
 ### 异步关闭
 
+通过传入`on-close`回调函数，可以自定义两侧滑动内容关闭时的行为
+
 ```html
 <van-swipe-cell :on-close="onClose">
-  <van-button
-    square
-    slot="left"
-    type="danger"
-    text="选择"
-  />
-  <van-cell
-    :border="false"
-    title="单元格"
-    value="内容"
-  />
-  <van-button
-    square
-    slot="right"
-    type="danger"
-    text="删除"
-  />
+  <template slot="left">
+    <van-button square type="primary" text="选择" />
+  </template>
+
+  <van-cell :border="false" title="单元格" value="内容" />
+
+  <template slot="right">
+    <van-button square type="danger" text="删除" />
+  </template>
 </van-swipe-cell>
 ```
 
 ```js
 export default {
   methods: {
+    // clickPosition 表示关闭时点击的位置
     onClose(clickPosition, instance) {
       switch (clickPosition) {
         case 'left':
@@ -114,7 +102,7 @@ export default {
 | 参数名 | 说明 | 类型 |
 |------|------|------|
 | clickPosition | 关闭时的点击位置 (`left` `right` `cell` `outside`) | `String` |
-| instance | SwipeCell 实例 | `Object` |
+| instance | SwipeCell 实例，用于调用实例方法 | `Object` |
 | detail | 额外信息，包含 name 字段 | `Object` |
 
 ### 方法