!20670 FIX：补充select组件 api 接口使用示例

Merge pull request !20670 from sunjiakun/select_doc

zh-cn/application-dev/reference/arkui-ts/ts-basic-components-select.md

@@ -88,6 +88,7 @@ struct SelectExample {
         .optionFont({ size: 16, weight: 400 })
         .space(this.space)
         .arrowPosition(this.arrowPosition)
+        .menuAlign(MenuAlignType.START, {dx:0, dy:0})
         .onSelect((index:number, text: string)=>{
           console.info('Select:' + index)
           this.index = index;