Nix flake example -- multiple dev shells

This repo holds a nix flake with multiple development shells, all targeting macOS non-ARM systems.

There are three language-specific shells:

• python includes a python interpreter, poetry, and black
• javascript includes a node interpreter, prettier, yarn, and eslint
• java includes sbt and openjdk-11

There's also an "omnishell" that includes all of the dependencies of the distinct shells.

The shells are presented in a nix flake. To use any of them, you'll need to:

• install the nix package manager (this can be done safely and won't affect anything else in your system)
• enable flakes support by adding experimental-features = nix-command flakes to $HOME/.config/nix/nix.conf
• fire up one of the shells: nix develop .#javascript (or .#python, .#java, or .#omnishell)

I didn't mess with golang here because I don't know any of the needed tools, but if you need to work with golang in nix, there's an excellent series of blog posts on golang with nix flakes. Really I think it's a great series for nix flakes in general as well, but it builds a go project, and I wasn't interested in that part at the time I read it.