Nav Menu Description?

The documentation states “To add description to your menu items, use the Description field. The descriptions will appear on your website underneath your menu items.” – But, my menus only have “Navigation Label” and “Title Attribute Fields”.

How do I enable the option to add the description so that I can have an extended menu description under the label; such as “clean & uncluttered” as shown in your demo on: http://demo.thematosoup.com/gumbo/

Thanks,
Randy