Take Salwa out of town.  Straight on at Decoration the LEFT at next roundabout.  Straight on at the next roundabout and you're on Wholesale Market  Street.  The animal market is on your left and you'll pass Qatar Scientific Club on your right.  Then you go past a decorative wall and gatehouse.  Turn RIGHT at the end of this wall, just before the Technical school.  The road bends left around the back of the school and QDC is on the right just after the bend.  It's a long detour if you overshoot the turning so if you're in any doubt it's better to turn too soon and rejoin the main road if you get it wrong.