Update README_CN.md

@@ -146,6 +146,7 @@ import 'package:flutter_screenutil/flutter_screenutil.dart';
   Widget build(BuildContext context) {
     //设置适配尺寸 (填入设计稿中设备的屏幕尺寸) 假如设计稿是按iPhone6的尺寸设计的(iPhone6 750*1334)
     ScreenUtil.instance = ScreenUtil(width: 750, height: 1334)..init(context);
+    
     print('设备宽度:${ScreenUtil.screenWidth}'); //Device width
     print('设备高度:${ScreenUtil.screenHeight}'); //Device height
     print('设备的像素密度:${ScreenUtil.pixelRatio}'); //Device pixel density