Amazon’s massive Buy Two, Get One Free sale is back as an early Prime Day deal just in time to stock up your summer reading list. To take advantage of this deal, add three eligible books to your cart; you’ll then receive a discount on the lowest-priced item at checkout. Most eligible books are also seeing big price cuts in addition to the B2G1 promotion, meaning you can save quite a bit while the deal is available. Dozens of novels,…