This text can be added via the "Text" section on the Customize Journal Style page.
But hmm. The location of that option depends on what layout the user is using. Many layouts (Digital Multiplex, Flexible Squares, Haven, Expressive, Expressive Winter, Mixit, Minimalism, Smooth Sailing) have it in the "Sidebar" section, some (3 Column, Quite Lickable, Disjointed, Opal, Refried Paper) have it in the "Text" section, one layout (Unearthed) has it in the "Display" section and one (Component) in the "Components" section.
I don't really have a suggestion on how to correct the FAQ, I just feel that at the moment it's a bit misleading, especially when it has a direct link to the "Text" section, and for many layouts the option isn't there.