Add HLSL doc

[marty-johnson59]

Let's include a document for HLSL (landing page) that explains how it can be used in Vulkan with links to the Microsoft documentation for reference

[SaschaWillems]

We already have something that may we can reuse in the guide: https://github.com/KhronosGroup/Vulkan-Guide/blob/main/chapters/hlsl.adoc

I wrote that one some time ago, and if there's something missing I'm happy to add.

The only question then is how we put it in a more prominent spot in the docs site :)

[marty-johnson59]

Yah, let's discuss on the next docs meeting. Perhaps we just have our docs drop-down link here.. Alternatively, we could have "HLSL Docs" in our drop down that goes to a brief landing page with pointers to Microsoft's docs (if they're useful) - as well as linking to your guide entry..

[marty-johnson59]

This is "done". We linked to the Guide page which has been updated w/ links to Microsoft docs. Let's close