- Clarify requirement of Vulkan 1.1 support in Vulkan Loader and ICDs
- Add a list of Vulkan extensions required for Wayland
- Document option to provide a custom implementation of the wsialloc.h
  interface and to disable support for VK_EXT_headless_surface
- Fix link to Vulkan Loader documentation

Change-Id: I791577a49570855fde86b2ffb1ac8e966f2073d9