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 module creates /etc/machine-id and/or /var/lib/dbus/machine-id. By
default, it is enabled and creates both files, making the latter a
symlink to the former.
