contrib: Update style guide and add Git rules
contrib: Update style guide and add Git rules

Change-Id: I968e503c0c9c107d5e4496e54f68e0e57563fec2

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