Yep I'm just a fan and minor contributor to Docker. Thought it was interesting to see a book so early but I do agree it's probably too early. Docker is changing fast. Version 0.5 should likely be out today.
It is on github, and pull requests are welcome. It is currently written for Docker 0.5. I will keep it up to date, and when we hit 1.0 I'll look at getting some hard copies made, if there is a demand.
I still need to pick a license, not sure what is best for a book, open to suggestions.