Update 'README.md'

README.md

@@ -5,3 +5,7 @@ This is a Flutter project to copy Dou Yin (which named Tik Tok overseas).
 
 # Demo for the recommend page. 推荐页面效果图
 ![image](https://pic4.zhimg.com/80/v2-27a3d4e7af10b0193848725c1885f10f_hd.jpg)
+
+## Reference
+
+https://github.com/todother/flutter_douyin_demo