Update systemd docs (#316)
Update systemd docs (#316)

* Updated examples for use with SystemD

As discussed in [here](https://github.com/bitwalker/distillery/issues/310).
- Remove the recommendation to set `RemainAfterExit=yes`. This doesn't seem to be necessary and prevents SystemD from restarting your app if it crashes.
- We already had examples for running app in foreground mode and running it as a daemon having SystemD attempt to guess the pid. I've added a third example configuration for using SystemD with a pidfile, if you don't want to use foreground and want your app restarted after crashes this is the way to go.
- Add notes about the strengths and weaknesses of the three approaches.

* Update Use With systemd.md

bitwalker/distillery,bitwalker/distillery