Updated README.md with create<memory_layout> and custom struct example
Updated README.md with create<memory_layout> and custom struct example

- create has changed, memory_layout is a template argument.
- added custom struct usage example.

aonorin/vulkan-cpp-library,google/vulkan-cpp-library,gardell/vulkan-cpp-library,gardell/vulkan-cpp-library,aonorin/vulkan-cpp-library,aonorin/vulkan-cpp-library,google/vulkan-cpp-library,google/vulkan-cpp-library