Add More Details to README?

I just went through the process of removing preact-compat from my existing app which was using react-router. I used this repo as a guide but I stumbled around awhile before I realized that all I had to do was copy `lib/react.js` into my project and modify `modulesDirectories` in the webpack config.

Since this is one of the top search results for 'preact react router' it would be awesome if some of these details could be added to the readme. Also `modulesDirectories` no longer exists in webpack 2.

Let me know if I can help.