style guide - calling the "User Guide" the "User Guide" instead of the "User and Administrator Guide"

Style guide: removing bit about all caps -- couldn't find an example of that in practice in the User Guide

Honestly I don't understand what this section is asking documentation
editors to do. If want this section back in, perhaps you could add some
clarification?

Importing "Book Style Guide" wiki page from https://wiki.civicrm.org/confluence/display/CRM/Book+style+guide