Add flake.nix (#226)

* Add nix flake support

* Use derivation from nixpkgs in flake

---------

Co-authored-by: b3nj5m1n <b3nj4m1n@gmx.net>

.gitignore

@@ -1,2 +1,4 @@
 dist-newstyle
 .stack-work
+result/
+result

flake.nix

@@ -0,0 +1,37 @@
+{
+  inputs = {
+    nixpkgs.url = "nixpkgs";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+  }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        runtimeDependencies = with pkgs; [
+          glow
+          jq
+        ];
+        overlays = [
+          (self: super: {
+            xdg-ninja = super.xdg-ninja.overrideAttrs (old: {
+              version = "git";
+              src = ./.;
+            });
+          })
+        ];
+        pkgs = import nixpkgs { inherit system overlays; };
+      in rec {
+        packages = flake-utils.lib.flattenTree {
+          xdg-ninja = pkgs.xdg-ninja;
+        };
+        defaultPackage = packages.xdg-ninja;
+        apps = {
+          xdg-ninja = flake-utils.lib.mkApp { drv = packages.xdg-ninja; };
+        };
+        defaultApp = apps.xdg-ninja;
+      }
+    );
+}