chore(docs): Add Usages section (Nix Flakes)

README.md

@@ -2,6 +2,54 @@
 
 Easily manage git hooks with Nix, internally using lefthook.
 
+## Usages
+
+### Nix Flakes
+
+```nix
+{
+  description = "An example nix flake project";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+
+    lefthook = {
+      url = "github:sudosubin/lefthook.nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.flake-utils.follows = "flake-utils";
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, lefthook, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+
+      in
+      {
+        checks = {
+          lefthook-check = lefthook.lib.${system}.run {
+            src = ./.;
+            config = {
+              pre-commit.commands = {
+                nixpkgs-fmt = {
+                  run = "${pkgs.nixpkgs-fmt}/bin/nixpkgs-fmt {staged_files}";
+                  glob = "*.nix";
+                };
+              };
+            };
+          };
+        };
+
+        devShell = nixpkgs.legacyPackages.${system}.mkShell {
+          inherit (self.checks.${system}.lefthook-check) shellHook;
+        };
+      }
+    );
+}
+```
+
 ## Credits
 
 This project was written with a lot of influence from [pre-commit-hooks.nix](https://github.com/cachix/pre-commit-hooks.nix).