It’s the next step in the biggest celebrity story of the year. It’s the long-awaited debut of Caitlyn Jenner’s docuseries charting her new life as a transgender woman. Fittingly, “I Am Cait” opens with the former Bruce Jenner, her ample tresses in huge rollers, at home getting hair-and-makeup treatment as she beholds a giant blowup of her bombshell Vanity Fair cover that followed her April interview with Diane Sawyer.