systemd timers

[xenoterracide]

instead of requiring cron, it'd be nice if systemd timer's could be used, instead of requiring 2 time keeping systems. I believe most linux OS's use systemd now. Obviously it could be an option. It's also worth noting that your readme talks about scheduled and offline for desktops. A systemd timer can resume a missed timer as soon as the system becomes available, and so this becomes a non issue.

[ludvigng]

I've created a pull request with systemd timers: #787