Fix URLs in GitHub authentication documentation

The live documentation site currently outputs dirty HTML tags due to bad Markdown parsing: 
![screen shot 2014-11-24 at 7 07 29 pm](https://cloud.githubusercontent.com/assets/2161/5175776/4a689d7a-740d-11e4-9faf-aaf0289632ef.png)

Using raw HTML links inside the `<table>` tags fixes it.