docs: Update i18n.zh-CN.md (ant-design#48138)

add two lines for import dayjs i18n.
that's an explain for date-picker's i18n wasn't effective

Signed-off-by: zhuxq <[email protected]>

Author: zxq08

docs/react/i18n.zh-CN.md

@@ -13,6 +13,8 @@ antd 提供了一个 React 组件 [ConfigProvider](/components/config-provider-c
 
 ```jsx
 import zhCN from 'antd/locale/zh_CN';
+// for date-picker i18n
+import 'dayjs/locale/zh-cn';
 
 return (
   <ConfigProvider locale={zhCN}>