Expand on shaders in Vulkan and add HLSL support

[SaschaWillems]

Shaders are touched on very lightly with a main focus on GLSL. It would be great to expand on how shaders fit into Vulkan and show alternatives to GLSL like HLSL.

Proposal: https://docs.google.com/document/d/1JGQY0NEk1X-J8kLSxj-gBx-AGZXAngFp_lPjg15otTM

Note: Copied from the old repo's project board

[SaschaWillems]

No longer required with #61