If you only have one or two manual, you migth want to just link to that one directly from the menu. This way, your user don't have to browse to a list of just one or two manuals. There is enough room in the menu for at least 3-4-5 direct links.
The system will automatically put your link last in the list, but you can edit the sort-order on page 2, as well as choose a font-awesome icon if you want that. Note that you only see the advanced settings below after you have created the simple link.