Update README.md

Author: gaearon

README.md

@@ -133,6 +133,8 @@ Refer to the [React documentation](https://facebook.github.io/react/docs/typeche
 
 Check out [Migrating from React.PropTypes](https://facebook.github.io/react/blog/2017/04/07/react-v15.5.0.html#migrating-from-react.proptypes) for details on how to migrate to `prop-types` from `React.PropTypes`.
 
+Note that this blog posts **mentions a codemod script that performs the conversion automatically**.
+
 There are also important notes below.
 
 ## How to Depend on This Package?