PBS is suddenly getting very timely. Even while we’re all enjoying the Roosevelts, there are still topical considerations. Next Tuesday, American Masters will show “Joan Rivers: A Piece of Work,” the highly praised doc about the comedian made by Ricki Stern and Annie Sundberg in 2010. “A Piece of Work” will air at 10:3opm right after Timothy Greenfield-Sanders’ “Boomer List.” Stern and Sundberg have made several other well received docs, and Stern was a family friend of Rivers. The film premiered at Sundance, and is notable for the access Rivers gave the women. You will learn a lot about her, and of course, there are plenty of laughs. Good for PBS!