improve page button on documentation

This should help engaging users to edit our documentation.

![imrp](https://f.cloud.github.com/assets/89049/1832835/94e7a5b2-73be-11e3-9e18-92e2c4ecab4f.png)
GitHub tells the users to create a fork!
![wikidoc](https://f.cloud.github.com/assets/89049/1832834/92bb898e-73be-11e3-8aa7-c630dfcd350e.png)