added warnings module

lib/option-warnings.nix

@@ -0,0 +1,31 @@
+{ lib, ... }:
+with lib;
+
+rec {
+  mkDeprecatedOption =
+    { option # an array of the path to the option
+    , alternative ? null
+    , message ? null
+    , visible ? false
+    , ...
+    }:
+    { options, ... }:
+    let
+      fromOpt = getAttrFromPath option options;
+      fullMessage = "The option `${showOption option}` has been deprecated." +
+        (optionalString (alternative != null) " You may want to use `${showOption alternative}` instead.") +
+        (optionalString (message != null) " Message: ${message}");
+    in
+    {
+      options = setAttrByPath option
+        (mkOption {
+          inherit visible;
+          description = fullMessage;
+        });
+      config = mkIf (fromOpt.isDefined) {
+        warnings = [
+          ("Nixvim: ${fullMessage}")
+        ];
+      };
+    };
+}