add note explaining by v4-shims are loaded

Author: mojavelinux

src/js/vendor/fontawesome.bundle.js

@@ -1,5 +1,6 @@
 ;(function () {
   'use strict'
+  // NOTE: v4-shims are required to support the output of the icon macro generated from AsciiDoc content
   require('@fortawesome/fontawesome-free/js/v4-shims')
   var fa = require('@fortawesome/fontawesome-svg-core')