message: Update viewer's readme
diff: @@ -15,6 +15,7 @@ Options:
  =simple - Simple ray casting kernel
  =whitted - Whitted style ray tracing kernel
  =pathtracing - Pathtracing global illumination kernel
  + =costs - BVH cost kernel
  -ambient Ambient color
  -bgcolor Background color
  -bounces=<ARG> Number of bounces for recursive ray tracing
  