add collapsed faq

ref: #13953

components/collapse/index.en-US.md

@@ -34,3 +34,9 @@ A content area which can be collapsed and expanded.
 | header | Title of the panel | string\|ReactNode | - |
 | key | Unique key identifying the panel from among its siblings | string | - |
 | showArrow | If `false`, panel will not show arrow icon | boolean | `true` |
+
+## FAQ
+
+### How to let the arrow to be on the right?
+
+You can adjust style of the arrow: <https://codesandbox.io/s/vpm8qwo37>

components/collapse/index.zh-CN.md

@@ -31,3 +31,9 @@ cols: 1
 | forceRender | 被隐藏时是否渲染 DOM 结构 | boolean | false |
 | header | 面板头内容 | string\|ReactNode | 无 |
 | key | 对应 activeKey | string | 无 |
+
+## FAQ
+
+### 我希望箭头在右边，怎么做？
+
+通过样式调整，将箭头放到右边就行啦：<https://codesandbox.io/s/vpm8qwo37>