Docs: Improve JSDoc for zxcvbn-async.js.

Props manuelaugustin, igorsch, LisanneKluitmans.
Fixes 43948.


git-svn-id: https://develop.svn.wordpress.org/trunk@43333 602fd350-edb4-49c9-b593-d223f7449a82

src/js/_enqueues/lib/zxcvbn-async.js

@@ -1,4 +1,11 @@
 /* global _zxcvbnSettings */
+/**
+ * Loads zxcvbn asynchronously by inserting an async script tag before the first
+ * script tag on the page.
+ *
+ * This makes sure zxcvbn isn't blocking loading the page as it is a big
+ * library. The source for zxcvbn is read from the _zxcvbnSettings global.
+ */
 (function() {
   var async_load = function() {
     var first, s;