Docs: Update info from js.md regarding plugins.js

Ref h5bp/html5-boilerplate#1558

doc/js.md

@@ -102,6 +102,11 @@ This file can be used to contain all your plugins, such as jQuery plugins and ot
 
 One approach is to put jQuery plugins inside of a `(function($){ ... })(window.jQuery);` closure to make sure they're in the jQuery namespace safety blanket.
 
+By default the `plugins.js` file contains a small script to avoid `console`
+errors in browsers that lack a `console`. The script will make sure that, if
+a console method isn't available, that method will have the value of empty
+function, thus, preventing the browser from throwing an error.
+
 ## vendor
 
 This directory can be used to contain all 3rd party library code.