TODO

Detect different types of MS Windows;
Detect old Linux distros without using os-release
  https://github.com/cfengine/core/blob/4f5e8dd65c4eccd69bc6fe603343233fe1a1f577/libenv/sysinfo.c#L1287
Detect versions of OSes and distros;
Detect other init systems than just systemd;
Detect musl vs glibc
Detect busybox

use-devel-assertos should not add itself twice (update, if run a second time)

to detect openrc:

Gianni says: @DrHyde@fosstodon.org for openrc, you probably get /sbin/openrc-run, and a few lines mentioning /sbin/openrc in /etc/inittab, like:
    si::sysinit:/sbin/openrc sysinit
    rc::bootwait:/sbin/openrc boot
    l0u:0:wait:/sbin/telinit u
    l0:0:wait:/sbin/openrc shutdown
    l0s:0:wait:/sbin/halt.sh
    l1:1:wait:/sbin/openrc single
    l2:2:wait:/sbin/openrc nonetwork
    l3:3:wait:/sbin/openrc default
    l4:4:wait:/sbin/openrc default
    l5:5:wait:/sbin/openrc default
    l6u:6:wait:/sbin/telinit u
    l6:6:wait:/sbin/openrc reboot
    l6r:6:wait:/sbin/reboot -dkn