There's a huge amount of behind-the-scenes content for the book - alternate versions, concept art, reference imagery, and timelapses - but I can only offer it to you if you prove you have a copy of the book.
First, you'll need to log in to Patreon.
I know, another service to sign up for. But this is just how the website knows you're you, so it can show you the behind-the-scenes stuff - and so security professionals protect your login info, instead of leaving it to me! The only personal info this website will have on you is your Patreon username and a tickmark that you bought the book.
Once you're logged in, you'll be redirected back here to do a 3-question quiz to prove you have the book. That's it!
As a thank you for signing up (and buying the book), all book owners get one month free of special backer-only access. And hey, after that month, if you want to support the project with a little bit of money through Patreon? It'd be appreciated.