“Broadway Idiot” chronicles the journey of Green Day’s Billie Joe Armstrong as he transitions from performing at a punk rock concert in Madison Square Garden to debuting his musical “American Idiot” on Broadway, a mere ten blocks away but in a completely different realm. The film offers a behind-the-scenes look at the exhilarating process of adapting the hugely successful album into a punk rock musical, and ultimately reveals how the theatrical world profoundly changed Billie Joe.