home: calibre: add 'package' option

modules/home/calibre/default.nix

@@ -5,11 +5,13 @@ in
 {
   options.my.home.calibre = with lib; {
     enable = mkEnableOption "calibre configuration";
+
+    package = mkPackageOption pkgs "calibre" { };
   };
 
   config = lib.mkIf cfg.enable {
     home.packages = with pkgs; [
-      calibre
+      cfg.package
     ];
   };
 }