Documentation for systemd service files can be automatically viewed
using systemctl help servicename if this field is present. Thus add the
relevant man page, the local and online documentation to the
documentation key.
When systemd-python is not installed, systemd notification falls back to
using the systemd-notify for service notification. This cannot be used
however unless the unit has NotifyAccess=all set.
The particular use case for this is when Salt is installed using pip. We
don't put systemd-python into the requirements.txt because we can't be
sure that the minion supports systemd, so pip installs won't necessarily
have systemd-python available.
Declaring After=syslog.target is unnecessary by now because syslog is
socket-activated and will therefore be started when needed. Thus remove
the obsolete syslog.target from the systemd service files.
