Add default.nix file

[neunenak]

[neunenak]

This PR is intended to get ord into nixpkgs, and close out https://github.com/casey/ord/issues/1668 .

Tagging @Kodylow

[neunenak]

What's the difference between a shell.nix and a default.nix file? I guess a shell.nix is for development, and a default.nix is for creating a package?

default.nix is the standard filename convention for a nix build file in the Nixpkgs repo. I don't think nix tooling cares about the exact filename.

Also, how do we avoid having to keep a bunch of values in sync in the default.nix file? I've dealt with keeping package hashes in sync before, and it sucks super bad. If we don't have a way of keeping them in sync manually, then I won't bother to update the hashes on every release, and the default.nix will be stale. If that were the case, then I would move this to contrib/default.nix, but it would be nicer to keep them in sync automatically, or be able to omit them from the default.nix.

I'm honestly not sure what the standard best practices are here for a project that wants to maintain its own nix build file outside of nixpkgs. Maybe @Kodylow has some insight here? In any case, I mostly made this PR because this nix build file worked for me and should work for other people if they manually update the hash and version, so maybe it makes sense to just put this in contrib with instructions about how to manually adjust the version.

[casey]

@neunenak If we can't auto-update the hashes, let's put this in contrib and merge it as is. Seems fine to include and should be useful, even if the hashes get out-of-date.

[casey]

I think we need to figure out a way to keep the version and hashes in sync before merging this.