Some improvements from a fork

[gBasil]

I made a fork of this repo some time ago, adding support for an env property and a "quick and dirty" fix for module patching: https://codeberg.org/isgoinggreat/pnpm2nix-nzbr

Feel free to incorporate these into this repo or use them as a basis or in some other way, I wasn't sure if they'd be merged (especially the patch-related changes).