This book was published in 2005 so it won't have the latest info, but this book with cycling commentator Phil Liggett as a contributor should be authoritative and it's gotten good reviews on Amazon.com.
The product description says Tour de France for Dummies is a plain-English guide to the world's most famous-and grueling-bicycle race. It's an easy-to-follow, entertaining guide that demystifies the history, strategy, rules, techniques, equipment, and competitors in what is arguably the most grueling and intriguing multiday, multistage sporting event in the world.
Click here to see more and purchase. The Tour de France runs for three weeks so you should have plenty of time to read this book.