In the RR repository you can find rr.server systemd unit file. The structure of the file is the following:
[Unit]
Description=High-performance PHP application server
[Service]
Type=simple
ExecStart=/usr/local/bin/roadrunner serve -v -d -c <path/to/.rr.yaml>
Restart=always
RestartSec=30
[Install]
WantedBy=default.target
The only thing that user should do is to update ExecStart option with your own. To do that, set a proper path of roadrunner binary, required flags and path to the .rr.yaml file.
Usually, such user unit files are located in .config/systemd/user/. For RR, it might be .config/systemd/user/rr.service. To enable it use the following commands: systemctl enable --user rr.service and systemctl start rr.service. And that's it. Now roadrunner should run as daemon on your server.
Also, you can find more info about systemd unit files here: Link.