added metadata to Cargo.toml in order to release to crates.io

[Shalevos]

The repository has yet to be uploaded to crates.io . I added metadata as seen in our curv library to the Cargo.toml file. After this is merged I will add a new release and upload the repo.

[survived]

Here are instructions on publishing: https://doc.rust-lang.org/cargo/reference/publishing.html

According to the manual, this metadata is still missing: license, repository, keywords, and categories