fixed 34d9ecbc from https://gitee.com/houhaoyu/docs/pulls/16424

houhaoyu@huawei.com

修改customdialogcontroller文档
Signed-off-by: Nhouhaoyu <houhaoyu@huawei.com>
Change-Id: Ia72c0d96dc9b08ff9e426c65cf66500705bd3047

zh-cn/application-dev/reference/arkui-ts/ts-methods-custom-dialog-box.md

@@ -36,6 +36,7 @@ CustomDialogController(value:{builder: CustomDialog, cancel?: () => void, aut
 ```ts
 dialogController : CustomDialogController = new CustomDialogController(value:{builder: CustomDialog, cancel?: () => void, autoCancel?: boolean})
 ```
+**说明**：CustomDialogController仅在作为@CustomDialog和@Component struct的成员变量，且在@Component struct内部定义时赋值才有效，具体用法可看下方示例。
 
 ### open()
 open(): void