Added systemd service file and refactored main.py

[KJSain]

Hello!

First time open-source contributing. Let me know if I'm doing this wrong.

I switched the main.py to use the argparse library to facilitate easier argument parsing. I also added the service file that I created to use for Linux instead of using screen to offload the backgrounding of the service. I think this makes it more "Linux-y".

• Switched main.py to use argparse for cleaner code and easier argument additions for the future
• Added extras folder with systemd service file example

[sambanks]

Thanks heaps for this!

I didn't like the screen bits of the install guide so started doing this, then thought to check the issues.

Works great!