The `-z2` is annoying now since it's really a legacy; we've long
since supported typing `archive`. Convert the docs fully and
explain that.
Also do some (but not all) of the tests just to encourage newer tests to use
`archive` too.
Closes: #980
Approved by: jlebon
In particular, NixOS has changed somewhat, and Conda is worth
looking at. Also it seems reasonable to mention rpm-ostree /
Gnome Continuous.
Closes: #331
Approved by: cgwalters
This content currently lives here:
<https://wiki.gnome.org/Projects/OSTree/RelatedProjects>. Moving it
into the manual in Markdown:
- Makes it look better
- It's more useful alongside the rest of the docs
- Is much less crummy in general than the GNOME wiki