In spite of there being considerable documentation sometimes in the
config file, we go with CC0 because we don't want the notion of
'derived work' of a config file.
The example `settings.conf` is also CC0. Add some docs to
it while we're at it.
- The mitigations are slightly intrusive, and may clash
with other, similar mitigations (especially for initramfs,
the recommended solution is to configure the system with
the snippet outside of Calamares).
