layers: GH576, Update layer details doc
layers: GH576, Update layer details doc

Added entries for new attachment index tests and enums.

Change-Id: Ida1de0bffc544718e63ccf3641a09dbe577f3c4d

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