Add startup scripts

The addition of this startup scripts will have no consequence in binary, as they are not included (yet). The systemd version could be added to the Debian package in a future version. EDIT: I modified the build_deb script to add the systemd version in package.

Note that I tested the openrc version, but not the systemd one, as I do not have a systemd environment here. Anyway, I hardly modified a file already used by some Ğ1 users, so it should be correct. EDIT: Systemd script is now tested.

If this MR could be included in future v6, the startup scripts will be used by the Gentoo package to automatically add the service.