Sportswriters dream of the ultimate underdog story. Chapel Hill based Tim Crothers found it in Katwe, a giant slum in Kampala, Uganda. Phiona Mutesi is currently Uganda’s leading female chess player, but a few years ago, when Tim met her, she was a child in the slums with promise. She couldn’t read or write. She subsisted by selling corn. Some days she ate, some days she went hungry, but every day she played chess in a program set up by a Virginia aid organization. And she was brilliant at the game. Tim Crothers first told Phiona’s story for ESPN The Magazine. Now he’s written a book, “The Queen of Katwe” (Scribner/2012). Tim Crothers joins host Frank Stasio in the studio today.