Added Vulkan wiki documentation

[ninepoints]

In case anyone here is interested in using it or contributing:

https://wiki.libsdl.org/CategoryVulkan

[Rene_Dudfield]

Wonderful. Thank you very much.

[numanoid]

I noticed that the syntax section of SDL_Vulkan_GetInstanceExtensions has the wrong function name, other than that thanks for this helpful addition

[ninepoints]

@numaoid good catch! I fixed it just now and you’re welcome