loader: Clean up some things in the MD file
loader: Clean up some things in the MD file

Clean up some documentation in the LoaderAndLayerInterface
markdown.  Over the next few weeks, I'll be working on
cleaning up the format and language of this doc.

Change-Id: I7858981293de9befb34701c31542d88c664cd6d8

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