Add shell.nix for Nix(OS) users

[enderger]

This PR adds a shell.nix file for Nix(OS) users. In Nix, a shell.nix file is used to create a development environment with certain packages installed, in this case just Golang.

[driusan]

Thanks! Unfortunately, I've never used NixOS so I'm not really capable of reviewing this.

Is this a manually created file or one that's generated by some kind of tool? If it's manually created, maybe it could be tangled from a markdown block. That way, the text could include some explanation and links to relevant documentation included for people who are new to Nix (like myself.)

[enderger]

This is a manually created file, I’ll explain:

1. { pkgs ? import <nixpkgs> {} }: tells Nix to store the package collection as a variable called pkgs
2. pkgs.mkShell uses that variable to allow you to use nix-shell to allow developers to access a shell with the environment defined in the brackets.
3. buildInputs = with pkgs; [ go ]; tells Nix to have Golang installed in the shell.

I may be able to convert it to a Markdown block, however I’m not sure where to put that block.

[enderger]

I added a version which can be compiled from lmt, describing what it does.

[driusan]

Why did you remove this punctuation?

[enderger]

Ah, sorry about that. My master branch had some temporary changes made while testing the actions PR.

[driusan]

I'm still not sure I understand what the shell.nix is for, but I'm willing to take it on faith that it's useful for Nix users and merge this after the unrelated punctuation change is fixed.

You can also add yourself to the credits at the end of the README if you'd like.