docs: Contributing.md updates
docs: Contributing.md updates

Change-Id: I0253ecd6166d84188f4f1cc1523c8e87d46c8590

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