Add Ubuntu install command

Gotta give those Ubuntu/Debian users some love.  Assuming that anyone running a different distribution will be able to find the appropriate way to install.

![screen shot 2014-01-28 at 10 48 07 pm](https://f.cloud.github.com/assets/86842/2025609/56f76834-887f-11e3-8a38-b839d8876ff9.png)