Systemd services. These are sorted by some kind of category into
subdirectories. The sudirectories won't exist in the real
`/etc/systemd/system` unless they end `.wants` or something similar
and I forget to update this README file if that happens.

## Worth reading

* Waiting for network devices to have IP address (**I only use this for
cables**) https://wiki.freedesktop.org/www/Software/systemd/NetworkTarget/#cutthecraphowdoimakenetwork.targetworkforme
    * systemctl enable NetworkManager-wait-online.service
    * systemctl enable systemd-networkd-wait-online.service