Migrate removed docs to README

[Savio-Sou]

Problem

When this library was spun out from the Noir standard library as of noir-lang/noir#6749, the existing documentations of this library was removed from the Noir docs without relocation to a readable place.

Happy Case

Copy information from https://github.com/noir-lang/noir/blob/909b22bb20645761aabf8b40622aa79c6a96ed6a/docs/docs/noir/standard_library/cryptographic_primitives/schnorr.mdx that is relevant still into the README of this repository.

Project Impact

Nice-to-have

Would you like to submit a PR for this Issue?

No