I have attached a completely untested, probably broken, service file.
You may want to consult someone knowledgeable on systemd to check it
out to see if it works and is idiomatic.
[Unit]
Description=Database for name server runtime information
Documentation=man:resolvconf(8)
DefaultDependencies=no
# Is this right? I want to start when /run is available and
# stop on shutdown (but not before).
RequiresMountsFor=/run
Conflicts=shutdown.target
[Service]
RemainAfterExit=yes
ExecPreStart=/bin/mkdir -p /run/resolvconf/interface; /bin/touch
/run/resolvconf/postponed-update
ExecStart=/sbin/resolvconf --enable-updates
ExecStop=/sbin/resolvconf --disable-updates
