Add permalink

[403studio]

Add permalink to docs, so we can access with 'prev' and 'next'
without it we can only access this doc use http://facebook.github.io/react/docs/thinking-in-react.zh-CN.html
however in the file which named tutorial-zh-CN.md has designed like this:

---
id: tutorial-zh-CN
title: 教程
permalink: tutorial-zh-CN.html
prev: getting-started-zh-CN.html
next: thinking-in-react-zh-CN.html

---

[jimfb]

Thanks!

[keyz]

@jimfb BTW, I speak Mandarin so feel free to assign me if you need me to review docs/translations.