Issue description

Packages like kicad and notmuch are currently rather awkward in that they are C/C++ programs, but provide Python bindings. Currently there is no documentation in the nixpkgs users guide offering guidance on how these packages should be packaged. Given that these bindings are currently quite hard to use in scripts (requiring that the user manually set PYTHONPATH appropriately), it seems this should change.

The documentation should answer this question: How does one package a package such that, for instance, nix run nixpkgs.notmuch -c python -c 'import notmuch' will actually work?