* doc: improve fetchers overview, deduplicate readme content
* Improve caveat explanation and some fetchurl content
* move out consumer docs on source fetching
* move note on mirror URLs to the relevant section
this may be better suited for the `fetchurl` reference, but it's probably better to
just render that information into the manual. for now, because
- contributor documentation encourages mirrors
- we can expect contributors to dig into the source
- linking source files is trivial in in-code documentation
we leave it there.
* move instructions for updating hashes to the manual
* Add more clarity on text, reorganise source hash methods
---------
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
Co-authored-by: Dominic Mills-Howell <dominic.millz27@gmail.com>
Co-authored-by: lolbinarycat <dogedoge61+github@gmail.com>
Move the manpage-to-URL mapping to `doc/manpage-urls.json` so that we can
reuse that file elsewhere, and generate the `link-manpages.lua` filter from
that file.
Also modify the Pandoc filter so that it doesn't wrap manpages that are
already inside a link.
Keeping a Lua filter is essential for speed: a Python filter would
increase the runtime `md-to-db.sh` from ~20s to ~30s (but Python is not
to blame; marshalling Pandoc types to and from JSON is a costly operation).
Parsing in Lua seems tedious, so I went with the Nix way.
