[llvm] [DirectX] Documenting Root Signature Binary representation (PR #131011)

[Justin Bogner via llvm-commits]

https://github.com/bogner commented:

Mostly good except I think the root parameter headers part is a bit misleading as currently worded.

It might also be helpful to describe the layout with a table. Do you think something like this would help?

| Part                   | Size                        |
|------------------------|-----------------------------|
| Root Signature Header  | 24 bytes                    |
| Root Parameter Headers | 12 bytes each               |
| Root Parameters        | 8, 12, 20, or 24 bytes each |
| Static Sampler         | 52 bytes each               |

There might be a better way to show this, feel free to play around with it if you have better ideas.

https://github.com/llvm/llvm-project/pull/131011