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.

先阅读 README 和其中引用的 lib/react.js，然后检查 issue 中提到的 webpack 配置细节，包括 modulesDirectories。更新 README，补充使用 React Router 和 Preact 的步骤，并注明 modulesDirectories 在 webpack 2 中不可用；当迁移指南清晰且准确时，即表示完成。

由索引模型根据 Issue 内容生成。