OSMC on Raspberry Pi 2 start at boot

You could use systemd: Implementing Sonarr with systemd

also: https://github.com/Sonarr/Sonarr/wiki/Autostart-on-Linux#method-4-rclocal

and for debian (pre-systemd): https://github.com/Sonarr/Sonarr/wiki/Autostart-on-Debian