Add Dusk additions to README

[HDauven]

Resolves #122

[moCello]

I think it would be nice to have a similar disclaimer as in the bls-lib:

⚠️ THIS CRATE IS A FORK OF https://github.com/zkcrypto/bls12_381: The Dusk team has added a variety of tools required for its own uses on the top of the original library. You SHOULD NOT use this library unless you need a specific tool that we've implemented and is not available in the original.

[HDauven]

I think it would be nice to have a similar disclaimer as in the bls-lib:

⚠️ THIS CRATE IS A FORK OF https://github.com/zkcrypto/bls12_381: The Dusk team has added a variety of tools required for its own uses on the top of the original library. You SHOULD NOT use this library unless you need a specific tool that we've implemented and is not available in the original.

Added with a slight modification 👍

[moCello]

LGTM