The new documentary “Anonymous Club” pulls the curtain back on the life of an introverted DIY artist experiencing — and going on tour in the aftermath of — an unpredictable and dizzying level of almost instantaneous success. Shot over three years, the film follows Australian singer-songwriter Courtney Barnett on tour through Europe, Asia and the States, performing to huge crowds, and grappling with her own anxiety and anhedonia. Filmmaker Danny Cohen tasked her with keeping an audio diary through the whole process, and her narration dots the film in ways that are witty, moving, sad and wistful. Here, in front of a sold-out theater, we discuss the making of the film, her role as an artist, persevering and what’s coming next.