Add unstable flake input

flake.lock

@@ -16,9 +16,26 @@
         "type": "github"
       }
     },
+    "nixpkgs-unstable": {
+      "locked": {
+        "lastModified": 1703499205,
+        "narHash": "sha256-lF9rK5mSUfIZJgZxC3ge40tp1gmyyOXZ+lRY3P8bfbg=",
+        "owner": "Nixos",
+        "repo": "nixpkgs",
+        "rev": "e1fa12d4f6c6fe19ccb59cac54b5b3f25e160870",
+        "type": "github"
+      },
+      "original": {
+        "owner": "Nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-unstable": "nixpkgs-unstable"
       }
     }
   },

flake.nix

@@ -4,10 +4,12 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.11";
                  # ^^^^^^^^^^^^^ this part is optional
+    nixpkgs-unstable.url = "github:Nixos/nixpkgs/nixpkgs-unstable";
   };
 
   outputs = { self, nixpkgs }: 
   let
+    # i don't define system here because each system should be defined in here
     lib = nixpkgs.lib;
   in {
     nixosConfigurations = {