Readme: Add info on pacman packages
python: Make sure we specify python2

* python3 causes extensive errors
* the python2 binary exists on all of
  my test systems (even when python3
  isn't installed)
* solves gh issue #58
Merge pull request #59 from kallisti5/master

Fixes for python 3 environments, add ArchLinux notes to readme. Thanks kallisti5 for this work!