This touches up a handful of places in the python documentation to try to make
the current best-practices more obvious. In particular, I often find the
function signatures (what to pass, what not to pass) confusing and have added
them to the docs.
Also updated the metas to be more consistent with the most frequently used
modern style.
Use example package `zerobin` instead of `bepasty-server` which
is no longer part of python-packages.
This fixes the examples for current nixpkgs versions.
1. Use the same approach like in the overlay example:
Override `python` instead of `pythonPackages` so that
`python.pkgs` refers to the new package set like `pythonPackages`.
This also fixes a bug in the original example where
`pkgs.fetchgit` was not in scope.
Add an extra example to illustrate how to override just a
package set.
2. Fix mix-up between `super` and `self` in the explanation text.
Also, simplify the explanation.
