Make NOTES_DIRECTORY configurable per host

nix/modules/home-manager/features/cli/notes.nix

@@ -1,12 +1,31 @@
-{ pkgs, ... }:
-
 {
-  home = {
-    packages = with pkgs; [ notes ];
+  config,
+  lib,
+  pkgs,
+  ...
+}:
 
-    sessionVariables = {
-      NOTES_DIRECTORY = "$DOCUMENTS/wiki/notes";
-      WIKI_DIRECTORY = "$DOCUMENTS/wiki";
+with lib;
+
+let
+  cfg = config.features.cli.notes;
+in
+{
+  options.features.cli.notes = {
+    enable = mkEnableOption "Enable notes";
+
+    directory = mkOption {
+      type = types.str;
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home = {
+      packages = with pkgs; [ notes ];
+
+      sessionVariables = {
+        NOTES_DIRECTORY = "${cfg.directory}";
+      };
     };
   };