When you: `sudo sv down /etc/service/syncthing/` the `TERM` signal
isn't propogated or trapped, so syncthing is orphaned and adopted by
init (PID 1).
- Changed call to `chpst` to `exec`
- Moved logging to `log/run` per `runsv` standard
Some distros (Ubuntu, Debian?) don't link `chpst` to `setuidgid`, as it
could conflict with djb daemontools installation. If daemontools isn't
going to be referenced in the README, then the example runit config
should reference the runit packaged utility.