Elm Packages Tooling and Upgrades with Nix

1st chunk of `pkgs/development/compilers/elm/packages/README.md`

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# Elm packages

Mixtures of useful Elm lang tooling containing both Haskell and Node.js based utilities.

## Upgrades

Haskell parts of the ecosystem are using [cabal2nix](https://github.com/NixOS/cabal2nix).
Please refer to [nix documentation](https://nixos.org/nixpkgs/manual/#how-to-create-nix-builds-for-your-own-private-haskell-packages)
and [cabal2nix readme](https://github.com/NixOS/cabal2nix#readme) for more information. Elm-format [update scripts](https://github.com/avh4/elm-format/tree/master/package/nix)
is part of its repository.

Node dependencies are defined in [node-packages.json](node/node-packages.json).
[Node2nix](https://github.com/svanderburg/node2nix) is used for generating nix expression
from this file. Use [generate-node-packages.sh](node/generate-node-packages.sh) for updates of nix expressions.

Title: Elm Packages Tooling and Upgrades with Nix

Summary

This document describes the tooling and upgrade process for Elm packages, which utilize a mix of Haskell and Node.js utilities. Haskell components rely on `cabal2nix` for Nix builds, with specific update scripts for `elm-format`. Node.js dependencies are managed in `node-packages.json` and processed by `node2nix` to generate Nix expressions, updated via `generate-node-packages.sh`.