docs: Add module description

Author: lambdalisue

mod.ts

@@ -1,3 +1,14 @@
+/**
+ * Core types for [Fall](https://github.com/vim-fall/fall), a Vim/Neovim fuzzy
+ * finder plugin powered by [Denops](https://github.com/vim-denops/denops.vim).
+ *
+ * > [!WARNING]
+ * >
+ * > This module is intended for internal use only and is not meant for external
+ * > use.
+ *
+ * @module
+ */
 export * from "./action.ts";
 export * from "./coordinator.ts";
 export * from "./curator.ts";