nix: add package to flake

flake.nix

@@ -16,6 +16,13 @@
         nil = input.nil.packages.${system}.nil;
       in
       {
+        apps.default = {
+          type = "app";
+          program = "${neovim}/bin/nvim";
+        };
+
+        packages.default = neovim;
+
         devShells.default = pkgs.mkShell {
           packages = [
             neovim
@@ -23,5 +30,9 @@
             pkgs.stylua # lua formatter
           ];
         };
+
+        overlays = f: p: {
+          myneovim = neovim;
+        };
       });
 }