Demo on basic usage

Author: ZeeCoder

README.md

@@ -37,6 +37,8 @@ const App = () => {
 };
 ```
 
+[CodeSandbox Demo](https://codesandbox.io/s/use-resize-observer-basic-usage-nrp0w2r5z0)
+
 ## Passing in Your Own `ref`
 
 You can pass in your own ref instead of using the one provided.