The docs/ directory is special in GitHub, since it can be used to serve GitHub
Pages from, so there's a benefit to switching to it in order to expose it
directly as a website.
Updated references to it from the documentations themselves, from the
CONTRIBUTING.md file and from Meson build files.
On systemd systems seasoned admins might be surprised to see that the
init scripts and log files are gone. To ease the transition let's place
some README files there, that hopefully help clearing up the situation.
