The documentary “How to Die in Oregon” premieres tonight on HBO. The film follows a woman named Cody Curtis as she suffers from liver cancer and, ultimately, makes the decision to end her life. It’s a difficult subject. Yet critics have described this documentary as “uplifting” and even “life-affirming.” Peter Richardson is the director of “How to Die in Oregon.” He and Stan Curtis, the husband of the woman portrayed in the film, talk about the process of making the film and why the story needed to be told.