Update HMR docs to reference to Shakapacker docs

Author: ahangarha

README.md

@@ -804,9 +804,8 @@ TheRubyRacer [hasn't updated LibV8](https://github.com/cowboyd/therubyracer/blob
 LibV8 itself is already [beyond version 7](https://github.com/cowboyd/libv8/releases/tag/v7.3.492.27.1) therefore many serverside issues are caused by old JS engines and fixed by using an up to date one such as [MiniRacer](https://github.com/discourse/mini_racer) or [TheRubyRhino](https://github.com/cowboyd/therubyrhino) on JRuby.
 
 ### HMR
-Hot Module Replacement is [possible with this gem](https://stackoverflow.com/a/54846330/193785) as it does just pass through to Shakapacker. Please open an issue to let us know tips and tricks for it to add to the wiki.
 
-Sample repo that shows HMR working with `react-rails`: [https://github.com/edelgado/react-rails-hmr](https://github.com/edelgado/react-rails-hmr)
+Check out [Enabling Hot Module Replacement (HMR)](https://github.com/shakacode/shakapacker/blob/master/docs/react.md#enabling-hot-module-replacement-hmr) in Shakapacker documentation.
 
 One caveat is that currently you [cannot Server-Side Render along with HMR](https://github.com/reactjs/react-rails/issues/925#issuecomment-415469572).