Add more installation instructions

[Gjum]

Currently, there are only instructions for Arch Linux, but the program is known to also run on Debian-based distros and Mac OS. Instructions to install it on these systems should be added to the README.

If you get it to run on any new system not documented in the README, or find an easier way, please make a comment on this issue or drop me an email (code.gjum@gmail.com).

[ryanrc]

It might be worth specifying which version of pip/python to use for install. I've got both python 2.7 and 3.4 installed. So when I tried to use pip things wouldn't run because it's set for python 2.7 but using pip3 everything installed and ran fine.