One segment of the Boston Asian American Film Festival’s opening night film tells the story of the historical and cultural hub located just blocks from where BAAFF films typically screen. In the documentary “A Tale of Three Chinatowns,” leaders from Boston’s Chinatown, including Cynthia Yee, Paul Lee, Lydia Lowe, Tunney Lee (now deceased), and many others recount the neighborhood’s past and describe its impact on their lives.