Identify nix-shell shebangs for pre-commit

TL;DR: Please review and/or approve:

I’d appreciate a review to make sure we get this implementation 100% right. This is useful to make pre-commit's file detection mechanics work in a nix context.

I’m a nix veteran. LGTM

… would do to promote getting it merged, as well.

This is needed, as @domenkozar has started work on bringing pre-commit to the nix world:

By the way, if you’re missing your favorite interpreter, consider to do a PR on this file:

See also: