Remove git.io from setup instructions

git.io has no TLS support and is generally recommended against except
for casual short-linking. git.io is officially unfit for linking to https-URLs,
relevant email discussion with github support attached.

![screen shot 2014-11-07 at 12 36 19](https://cloud.githubusercontent.com/assets/47542/4952301/5bde706e-6672-11e4-83d1-d18100c9fa1a.png)

As a quick fix, I included the full URLs.

Also, on the same note: wouldn't it make sense to use specific revisions if the install scripts for automated building?