Update README with links to migration content

Author: BookOfGreg

README.md

@@ -8,6 +8,11 @@
 
 You are looking at the 2.3 stable branch. This branch is for maintaining the prebundled 15.6 ReactJS with Addons. Gem version 2.4.x onwards and master will no longer have React Addons.
 
+If you need to make changes for the prebundled react, see the migration docs here:
+https://reactjs.org/blog/2016/11/16/react-v15.4.0.html
+https://reactjs.org/blog/2017/04/07/react-v15.5.0.html
+https://reactjs.org/blog/2017/06/13/react-v15.6.0.html
+
 `react-rails` makes it easy to use [React](http://facebook.github.io/react/) and [JSX](http://facebook.github.io/react/docs/jsx-in-depth.html) in your Ruby on Rails (3.2+) application. Learn more:
 
 - React's [Getting Started guide](https://facebook.github.io/react/docs/getting-started.html)