Nix module: add package option

This allows users to set a different package, for example pkgs.matugen.

Co-authored-by: Amadej Kastelic <[email protected]>

module.nix

@@ -39,7 +39,7 @@ matugen: {
     cd $out
     export HOME=$(pwd)
 
-    ${pkg}/bin/matugen \
+    ${cfg.package}/bin/matugen \
       image ${cfg.wallpaper} \
       ${
       if cfg.templates != {}
@@ -57,6 +57,12 @@ in {
   options.programs.matugen = {
     enable = lib.mkEnableOption "Matugen declarative theming";
 
+    package =
+      lib.mkPackageOption pkgs "matugen" {}
+      // {
+        default = pkg;
+      };
+
     wallpaper = lib.mkOption {
       description = "Path to `wallpaper` that matugen will generate the colorschemes from";
       type = lib.types.path;