it is out of date, all over the place in level of detail, is really
about `nixpkgs`, and in general instructions should not be part of
a reference manual.
also:
- update redirects and internal links
- use "Nix language" consistently
This looks a lot better (and is also more semantically meaningful).
Since this list is generated in a Nix expression, I don't think using
HTML here is going to be the thing that puts people off modifying this
part of the documentation!