rewrite installation section to use pyproject.toml

[sjvrijn]

Changes in this PR

fixes #326

The section on creating an installable package has been rewritten to only assume pyproject.toml as the relevant file to specify everything in. I've also been a bit more elaborate about what is in pyproject.toml, since the build system landscape is a bit more stable than it used to be when this was originally written. Speaking of build-system, I've explicitly mentioned hatchling and setuptools as our recommendations, with a link to e.g. the python packaging guide for other options.

Checklist

SIGNIFICANT changes / additions, e.g. new chapters

• I discussed my contribution in an issue and took into account feedback.

ALL contributions

• I previewed my changes locally using e.g. python3 -m http.server 4000 and confirmed they work correctly.
• I checked for broken links, e.g. using the link checker GitHub Action workflow, or locally by using docker run --init -it -v pwd:/docs lycheeverse/lychee /docs --config=docs/lychee.toml, at least for the files I changed.
• My name was added to the CITATION.cff file.

[bouweandela]

Thanks!