Update README.md

Author: Zhouyuankun

Diff for: README.md

@@ -3,7 +3,7 @@
 This is a native macOS live wallpaper app, support Intel & Apple Silicon.
 
 Here is a demo in gif. The wallaper display quality is related to your video quality.
-![Live Wallpaper]()
+![Live Wallpaper](https://github.com/Zhouyuankun/ScreenZ/blob/main/resources/demo.gif)
 
 1. How to get this app?
 This is a Xcode project, you can run it on your Xcode. There is also a release DMG on page.