chore: update readme

Author: warmthsea

README.md

@@ -1,3 +1,8 @@
 # element-plus-demo
 
-Sandbox demo fork of vitesse-lite
+Sandbox demo fork of vitesse-lite. 
+💻 Preivew: https://element-plus-demo-rho.vercel.app
+
+#### Try it with code sandbox
+
+[![Edit element-plus](https://codesandbox.io/static/img/play-codesandbox.svg)]([https://codesandbox.io/s/element-plus-demo-dxtcr](https://codesandbox.io/p/github/element-plus/element-plus-demo/main))