add docs for exported symbols

src/mod.ts

@@ -5,7 +5,23 @@ export { None, Some, type Option } from './enum/option.ts';
 export { Err, Ok, type Result } from './enum/result.ts';
 
 // export some commonly used types
+
+/**
+ * The shorthand of Promise<Option<T>>.
+ */
 export type AsyncOption<T> = Promise<Option<T>>;
+
+/**
+ * The shorthand of Promise<Result<T, E>>.
+ */
 export type AsyncResult<T, E> = Promise<Result<T, E>>;
+
+/**
+ * The shorthand of Result<T, Error>.
+ */
 export type IOResult<T> = Result<T, Error>;
+
+/**
+ * The shorthand of Promise<Result<T, Error>>.
+ */
 export type AsyncIOResult<T> = Promise<IOResult<T>>;