document the render_cache more clearly
document the render_cache more clearly

wsw0108/Windshaft,manueltimita/Windshaft,wsw0108/Windshaft,CartoDB/Windshaft,CartoDB/Windshaft,HydroLogic/Windshaft,HydroLogic/Windshaft,manueltimita/Windshaft,HydroLogic/Windshaft,CartoDB/Windshaft,wsw0108/Windshaft,manueltimita/Windshaft