Merge pull request #1 from spkane/master

Add instructions on using pip to install ipcalc
Try to ensure we are logged into a Unix system before proceeding too far
Merge branch 'detect-non-unix' of github.com:spkane/Device42-AutoDiscovery-Scripts into detect-non-unix

* 'detect-non-unix' of github.com:spkane/Device42-AutoDiscovery-Scripts:
  Try to ensure we are logged into a Unix system before proceeding too far
Add instructions on using pip to install ipcalc