docs(readme): add usage as Nix package (#61)

Co-Authored-By: Ladas552 <[email protected]>

README.md

@@ -71,6 +71,38 @@ Options:
 
 Run `cargo install --release --path .` to compile and install Norgolith in your `~/.cargo/bin` directory.
 
+### 📦 Nix Package
+
+You can add norgolith to your NixOS configuration with flakes
+
+<details>
+<summary>Minimal flake.nix for a NixOS configuration:</summary>
+
+```nix
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+    norgolith.url = "github:NTBBloodbath/norgolith";
+  };
+  outputs =
+    { nixpkgs, norgolith, ... }:
+    {
+      nixosConfigurations.mysystem = nixpkgs.lib.nixosSystem {
+        modules = [
+          {
+          # add norgolith as a package
+            environment.systemPackages = [
+              norgolith.packages.x86_64-linux.default
+            ];
+          }
+        ];
+      };
+    };
+}
+```
+</details>
+
 ## ❄️ Developing and testing with Nix
 
 The Norgolith repository includes a Nix flake for development and testing purposes in the root directory. This section outlines how to