suggest add auto restart systemd file to readme

[playdougher]

I run uniclip client on Virtualbox VM, after saving the VM state and recovering it, the uniclip client fails. To ensure it restarts automatically after a failure, we can create a service file "/etc/systemd/system/uniclip.service":

[Unit]

Description=Uniclip Service
After=network.target

[Service]

ExecStart=<path of uniclip> <IP>:<port>
Restart=always
RestartSec=1
Environment=DISPLAY=:0

[Install]
WantedBy=graphical.target

to make uniclip to auto-start after boot, run systemctl daemon-reload ; systemctl enable uniclip.service --now