docs: add tips of get-contaienr in root node (#5078)

src/popup/README.md

@@ -112,6 +112,8 @@ export default {
 }
 ```
 
+> Tips: The get-container prop cannot be used on the root node
+
 ## API
 
 ### Props

src/popup/README.zh-CN.md

@@ -123,6 +123,8 @@ export default {
 }
 ```
 
+> 注意：使用 get-container 属性的组件不能为根节点
+
 ## API
 
 ### Props