Update README.md

Add link to CodeSandbox URL n README.

Author: simonswiss

README.md

@@ -36,6 +36,10 @@ To get started:
 
 4. Open `public/index.html` in your editor and start experimenting!
 
+## Play with it on CodeSandbox
+
+A CodeSandbox version of this playground [is one click away](https://codesandbox.io/s/github/tailwindcss/playground/tree/master)!
+
 ## Building for production
 
 Even though this isn't necessarily a starter kit for a proper project, we've included an example of setting up [cssnano](https://cssnano.co/) to optimize your CSS for production.