Add installation instructions

README.md

@@ -13,10 +13,41 @@ You include a small bash script inside your commit messages, and `git-check-asse
 
 ⚠️ Only run this on repositories and branches that you trust, since the `bash` scripts in the commit messages can do whatever they want.
 
-## Building
+## Installation
 
-```bash
+On most systems, clone this repository and add the `bin` directory to your `PATH`.
-nix build .
+
+If you use Nix with flakes, you can simply add it to your program's devshell instead:
+
+```diff
+@@ -2,12 +2,18 @@
+   inputs = {
+     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+     flake-utils.url = "github:numtide/flake-utils";
++    git-check-assertions = {
++      url = "git+https://codeberg.org/svenvanheugten/git-check-assertions.git?ref=main";
++      inputs.nixpkgs.follows = "nixpkgs";
++      inputs.flake-utils.follows = "flake-utils";
++    };
+   };
+   outputs =
+     {
+       self,
+       nixpkgs,
+       flake-utils,
++      git-check-assertions,
+     }:
+     flake-utils.lib.eachDefaultSystem (
+       system:
+@@ -17,7 +23,10 @@
+       {
+         packages.default = pkgs.callPackage ./default.nix { };
+         devShells.default = pkgs.mkShell {
+-          packages = [ ];
++          packages = [ git-check-assertions.packages.${system}.default ];
+         };
+       }
+     )
 ```
 
 ## Examples of commit messages