SHOP STEWARDS CORNER     Tonight we focus on a photo essay published by photo journalist James Oatway and jour-nalist Stephan Hofstatter on the life of food couriers in Joburg. It says - An army of riders ferry food around the South African city, their lives and travails largely unseen by the peo-ple they serve. Photojournalist James Oatway has spent several months documenting their challenges.     It’s published in today’s Guardian newspaper.     Joining me is    James Oatway  Photo-journalist