doc/python: clarify python nix tooling efforts
doc/python: clarify python nix tooling efforts

@garbas and @seppeljordan, are these updates correct?

I removed `offlinehacker/pypi2nix` as an unmaintained ancestor of the current repo `nix-community/pypi2nix`. It appears @garbas forked `offlinehacker/pypi2nix` to `garbas/pypi2nix` and then handed off maintainership to @seppeljordan, transferring the repo to `nix-community/pypi2nix`.
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