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.
I figure sooneror later we'll have more of these docs, hence let's give
them a clean place to be.
This leaves NEWS and README/README.md as well as the LICENSE texts in
the root directory of the project since that appears to be customary for
Free Software projects.
We *do* have the occasional security issue, where it would be nice to have
non-public disclosure and time to fix the issue before it's fully public. Our
github infrastracture does not make it easy to report vulnerabilities in
confidential manner, so let's leverage the distro mechanisms for that. I
think we're better off with this solution than leaving it up to individual
reporters to discover some mechanism on their own.