Update docs

index.d.ts

@@ -33,9 +33,9 @@ declare class JWT {
      * Returns the payload **without** verifying the integrity of the token. Please use `jwt.verify()` first to keep your application secure!
      * 
      * @param {string} token The token string generated by `jwt.sign()`.
-     * @returns {object | null} Returns payload `object`.
+     * @returns {JWTDecodeReturn} Returns an `object` containing `header` and `payload`.
      */
-    decode(token: string): object | null
+    decode(token: string): JWTDecodeReturn
 }
 declare const _exports: JWT
 
@@ -52,4 +52,9 @@ type JWTVerifyOptions = {
     throwError?: boolean
 }
 
+type JWTDecodeReturn = {
+    header: object,
+    payload: object
+}
+
 export = _exports