Documentation updates

[Allan Day]

Simon McVittie <smcv at collabora.com> wrote:
...
> > This week I've ported some of the pages from flatpak.org to docs.flatpak.org.
>
> If this is the same thing as https://github.com/flatpak/flatpak-docs/
> please could you put a copyright notice and license grant on it?
...

Urgh, I hadn't realised that it wasn't licensed. I guess we'll have to
get consent from all the authors in order to set a licence. :/

Allan