The cover of “Audrey and Bill” helpfully clarifies that it’s “A Romantic Biography of Audrey Hepburn & William Holden.” The two film stars met while co-starring in Billy Wilder’s effervescent 1954 rom-com, “Sabrina.” In that film, Hepburn plays the title character, the young daughter of the chauffeur to the filthy-rich Larrabee family; she pines for David Larrabee, played by Holden.