docs: added root jsdocs

src.ts/index.ts

@@ -1,4 +1,9 @@
-
+/**
+ *  The Application Programming Interface (API) is the collection of
+ *  functions, classes and types offered by the Ethers library.
+ *
+ *  @_section: api:API Specification
+ */
 import * as ethers from "./ethers.js";
 
 export { ethers };