Updates to the Install page

**Non-installable platforms**
![image](https://cloud.githubusercontent.com/assets/25212/3682067/f2c200c0-12c3-11e4-87d5-dc2b22985284.png)

**Installable platforms**
![image](https://cloud.githubusercontent.com/assets/25212/3682069/03c8f43c-12c4-11e4-88e1-6652d7f6aa24.png)

This has to be done before the env variable is used above.