Start script for OH2

@danielwalters86: I tried your systemd script following your instruction (you also PRed, however, on my Raspi 2 with Raspbian Jessie the command
sudo systemctl enable openhab2
always returns
Failed to execute operation: No such file or directory
assuming I’ve put my unit into a file openhab2.

As @jtmoderate876 suggested, I had to put the file not anywhere on the disk but exactly in /lib/systemd/system/ and had to suffix it with .service.