readme: update installation section

Add stable/unstable packages + nix

README.md

@@ -20,18 +20,52 @@ The main control script for the Caelestia dotfiles.
 
 ## Installation
 
-### Package manager (recommended)
+### Arch linux
 
-The cli is available from the AUR as `caelestia-cli-git`. To install it you can use
-an AUR helper like [`yay`](https://github.com/Jguer/yay), or manually download the
-PKGBUILD and run `makepkg -si`.
+The CLI is available from the AUR as `caelestia-cli`. You can install it with an AUR helper
+like [`yay`](https://github.com/Jguer/yay) or manually downloading the PKGBUILD and running `makepkg -si`.
 
-e.g. using yay
+A package following the latest commit also exists as `caelestia-cli-git`. This is bleeding edge
+and likely to be unstable/have bugs. Regular users are recommended to use the stable package
+(`caelestia-cli`).
+
+### Nix
+
+You can run the CLI directly via `nix run`:
 
 ```sh
-yay -S caelestia-cli-git
+nix run github:caelestia-dots/cli
 ```
 
+Or add it to your system configuration:
+
+```nix
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+
+    caelestia-cli = {
+      url = "github:caelestia-dots/cli";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+}
+```
+
+The package is available as `caelestia-cli.packages.<system>.default`, which can be added to your
+`environment.systemPackages`, `users.users.<username>.packages`, `home.packages` if using home-manager,
+or a devshell. The CLI can then be used via the `caelestia` command.
+
+> [!TIP]
+> The default package does not have the shell enabled by default, which is required for full functionality.
+> To enable the shell, use the `with-shell` package. This is the recommended installation method, as
+> the CLI exposes the shell via the `shell` subcommand, meaning there is no need for the shell package
+> to be exposed.
+
+For home-manager, you can also use the Caelestia's home manager module (explained in
+[configuring](https://github.com/caelestia-dots/shell?tab=readme-ov-file#home-manager-module)) that
+installs and configures the shell and the CLI.
+
 ### Manual installation
 
 Install all [dependencies](#dependencies), then install