Adding a systemd user service example file

[JordanPlayz158]

I have created a systemd user service file that starts ARRPC and I think it would be good to include it as an example in the repository. It is not perfect and could have improvements but I made it the best and most simple I could.

[Service]
Type=simple
ExecStart=/usr/bin/bash -c '/usr/bin/git fetch && /usr/bin/git pull && /usr/local/bin/npm install && /usr/bin/node src'
WorkingDirectory=/path/to/arrpc

[Install]
WantedBy=default.target

The only prerequisite is that you have cloned the ARRPC git repository yourself (and should go without saying, have the dependencies to run ARRPC installed) and to put this in your systemd user service folder (in my case ~/.config/systemd/user) and then execute systemctl --user enable --now arrpc