flake: add inputs option

Signed-off-by: saygo-png <saygo.mail@proton.me>

flake/default.nix

@@ -9,6 +9,7 @@
   imports = [
     ./flake-modules
     ./ci.nix
+    ./inputs.nix
     ./lib.nix
     ./nixvim-configurations.nix
     ./overlays.nix

flake/inputs.nix

@@ -0,0 +1,9 @@
+{ lib, inputs, ... }:
+{
+  options.inputs = lib.mkOption {
+    type = lib.types.raw;
+    description = "Flake inputs.";
+    readOnly = true;
+  };
+  config.inputs = inputs;
+}