On the big screen, the art world is often the object of sneering commentary about wealth and class. But “Showing Up”, released in American cinemas on Friday, is an account of ordinary artists, well, making art. Lizzy (Michelle Williams) is an introverted sculptor in Portland, Oregon, working as a receptionist by day and tending to her intricate clay sculptures by night. She also contends with the demands of her family and friends, most of whom have their own artistic inclinations.