[$] Understanding Nix flakes

Nix flakes are an experimental feature of the Nix package-management tool designed to build projects in a more self-contained and reproducible way. Despite the feature's experimental status, it has become increasingly popular for open-source projects to publish flake.nix files that offer predefined development environments and build automation even when those repositories may not offer an upstream package or module for the NixOS Linux distribution. Although Nix flakes have a complicated history, and the path for stabilization is uncertain, flakes can provide useful capabilities for projects that choose to include them.