add documentation for async form internationalization

static/js/utils/asyncForm.js

@@ -12,6 +12,11 @@
    * Example usage:
    *   <form uw-async-form method='POST' action='...'>
    *     ...
+   *
+   * Internationalization:
+   *  This utility expects the following translations to be available:
+   *    asyncFormFailure: text that gets shown if an async form request fails
+   *      example: "Oops. Something went wrong."
    */
 
   var ASYNC_FORM_UTIL_NAME = 'asyncForm';