layers: Update layer validation doc for CopyImage validation additions
layers: Update layer validation doc for CopyImage validation additions

Change-Id: I045076fc7990e72389a45b432ae099010f4f5d48

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools