systemd rrd_directory option

[benalexau]

PR #16 incorporated a systemd file that specified --rrd_directory=/var/lib/collectd. This makes it incompatible with installations that typically require this value be /var/lib/collectd/rrd, thus requiring file edits such reflected in my Sick Muse AUR package PKGBUILD.

Given both the RRDtool page and the SickMuse default use /var/lib/collectd/rrd, I suggest the systemd file should also use this directory.

[mlavin]

I'm 👍 on anything that can be done to make it easier for upstream package maintainers.