replace the aur package with a nix flake

flake.nix

@@ -0,0 +1,22 @@
+{
+  description = "Margin Calendar, a calendar for Google Calendar";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+    in
+    {
+      overlays.default = final: prev: {
+        margin-calendar = final.callPackage ./nix/package.nix { };
+      };
+
+      packages.${system} = {
+        margin-calendar = pkgs.callPackage ./nix/package.nix { };
+        default = self.packages.${system}.margin-calendar;
+      };
+    };
+}