flake.nix: add nix package

flake.nix

@@ -22,5 +22,20 @@
         ];
       };
     });
+
+    packages = forAllSystems (_: pkgs: {
+      default = lib.pipe ./main.py [
+        lib.readFile
+        (lib.splitString "\n")
+        lib.tail
+        (lib.concatStringsSep "\n")
+        (pkgs.writers.writePython3Bin "passwd2systemd-users" {
+          libraries = with pkgs.python3Packages; [ ];
+          flakeIgnore = [
+            "E501" # I absolutely love and adore long lines, please let every single line be above 80 characters please
+          ];
+        })
+      ];
+    });
   };
 }