I’m not sure why Goodreads hides their “Add a New Book” page from us. Are they afraid of some kind of literary hack? Or an avalanche of white papers? A storm of porn? Whatever the reason, just try to search for “add my book to goodreads” and you’ll find what you’re looking for waaaaaaay down on the search results page.
All you have to do is go to this url, and you’re set:
Simple post for a simple process. Made hard by Goodreads.
Good luck!