Systemd unit files

[fts-tmassey]

If anyone cares, I created a generic systemd unit file on my fork: https://github.com/fts-tmassey/SiriusXM

If someone chooses to use my updated script, there's also an override file you can look at that shows how I use environment variables to safely store my credentials yet still start the script automatically.

A big thank you to andrew0 for his script: it's awesome for me to now have SXM in every room of my house!