post_upgrade() {
  cat <<EOF
Starting from 1.1pre12, tinc ships its own systemd unit files, which are
different from previous ones:

1. Unit file name changes from tincd(@) to tinc(@)
2. Network without network name is not supported anymore
3. tinc.service now serves to start all tinc@.service

Please reload systemd and do appropriate configuration according to these
changes.
EOF
}