build(nix): import flake template

flake.nix

@@ -0,0 +1,55 @@
+{
+  description = "Flake for building the MacGregor House website";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    utils.url = "github:numtide/flake-utils";
+    mkElmDerivation.url = "github:jeslie0/mkElmDerivation";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      utils,
+      mkElmDerivation,
+    }:
+    utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs {
+          overlays = [ mkElmDerivation.overlays.mkElmDerivation ];
+          inherit system;
+        };
+      in
+      {
+        devShells.default =
+          with pkgs;
+          mkShell {
+            buildInputs = [
+              elmPackages.elm
+              elmPackages.elm-test
+              elmPackages.elm-format
+            ];
+          };
+
+        packages = {
+          default = pkgs.mkElmDerivation {
+            name = "macgregor";
+            src = ./.;
+            elmJson = ./elm.json;
+            nativeBuildInputs = [ pkgs.elmPackages.elm ];
+            buildPhase = ''
+              elm make src/Main.elm --output Main.js --optimize
+            '';
+            installPhase = ''
+              mkdir $out
+              cp Main.js $out
+            '';
+          };
+        };
+
+        formatter = nixpkgs.legacyPackages.${system}.nixfmt-rfc-style;
+      }
+    );
+}