Add default package to flake

So we can pull the package in more easily from other projects since
it's not in nixpkgs.

flake.nix

@@ -1,17 +1,38 @@
 {
   description = "geniveev dev shell";
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
-  inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    utils.url = "github:numtide/flake-utils";
+    gomod2nix = {
+      url = "github:tweag/gomod2nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.utils.follows = "utils";
+    };
+  };
 
-  outputs = { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem (system: let
-      pkgs = nixpkgs.legacyPackages.${system};
+  outputs = { self, nixpkgs, utils, gomod2nix }:
+    utils.lib.eachDefaultSystem (system:
+    let pkgs =  import nixpkgs {
+      inherit system;
+      overlays = [
+        gomod2nix.overlays.default
+      ];
+    };
     in {
+      packages.default = pkgs.buildGoApplication {
+        pname = "geniveev";
+        version = "0.1.1";
+        pwd = ./.;
+        src = ./.;
+        modules = ./gomod2nix.toml;
+      };
+
       devShells.default = pkgs.mkShell {
         packages = [
           pkgs.bashInteractive
           pkgs.go_1_20
           pkgs.goreleaser
+          gomod2nix.packages.${system}.default
         ];
       };
     });

gomod2nix.toml

@@ -0,0 +1,21 @@
+schema = 3
+
+[mod]
+  [mod."github.com/inconshreveable/mousetrap"]
+    version = "v1.1.0"
+    hash = "sha256-XWlYH0c8IcxAwQTnIi6WYqq44nOKUylSWxWO/vi+8pE="
+  [mod."github.com/pelletier/go-toml/v2"]
+    version = "v2.0.8"
+    hash = "sha256-wWxswr/lTq+McYbScmJM1ECKQ6eNJ5m44SM7TmrHThM="
+  [mod."github.com/spf13/afero"]
+    version = "v1.9.5"
+    hash = "sha256-+XECQxkx0P+ZaQDm4dQ6ItMtHMj+2uNemEC18dsdor0="
+  [mod."github.com/spf13/cobra"]
+    version = "v1.7.0"
+    hash = "sha256-bom9Zpnz8XPwx9IVF+GAodd3NVQ1dM1Uwxn8sy4Gmzs="
+  [mod."github.com/spf13/pflag"]
+    version = "v1.0.5"
+    hash = "sha256-w9LLYzxxP74WHT4ouBspH/iQZXjuAh2WQCHsuvyEjAw="
+  [mod."golang.org/x/text"]
+    version = "v0.10.0"
+    hash = "sha256-pt4Ce9+Bvf7f0Vo8oUZ71F1aSCcCxsx6Lg0cvanq7x8="