docs: Update Contributing.md for msg output info
docs: Update Contributing.md for msg output info

Change-Id: Iab9831c798970334808c5d0784e1e5128f05c6f6

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers