docs: add structure section to README

Closes #7.

README.md

@@ -4,6 +4,15 @@
     <img src="https://raw.githubusercontent.com/catppuccin/catppuccin/main/assets/palette/macchiato.png" />
 </div>
 
+## Structure
+
+- `home/apps/*` - configuration for GUI applications.
+- `home/programs/*.nix` - configuration for CLI programs.
+- `home/scripts/*.sh` & `home/scripts.nix` - custom symlinked shell scripts.
+- `home/variables.nix` - environment variables.
+- `icons/*.ico` - custom app icons for GUI applications.
+- `modules/packages.nix` & `modules/homebrew.nix` - packages from [Nixpkgs](https://github.com/NixOS/nixpkgs) and [Homebrew](https://brew.sh/), respectively.
+
 ## Credits
 
 Many thanks to [ryanccn/flake](https://github.com/ryanccn/flake), [isabelroses/dotfiles](https://github.com/isabelroses/dotfiles), and [nix-darwin-kickstarter](https://github.com/ryan4yin/nix-darwin-kickstarter) for inspiring and serving as the foundation for this configuration.