[docs] Document Determinism Properties #4466
Description
Is your feature request related to a problem? Please describe.
I've just been asked for the nth time whether zstd is deterministic and launched into the same spiel about "yes, but in a constrained way, and why are you asking??". This is a recurring siren call that our users want, and we should write up a description of the properties Zstd does and doesn't provide / an FAQ / guidance.
Describe the solution you'd like
We should write a doc we can link people to.
Describe alternatives you've considered
We could not do it.