docs for hasher states could use a reference to the `Digest` trait

For someone new to the ecosystem it might be hard to tell how to use a... For example, sha3::Keccak256 (https://docs.rs/sha3/latest/sha3/type.Keccak256.html), it's just a type alias with no real info about what it is (other than some nebulous "hasher state") or how to use it. I'd recommend linking to the Digest trait in the docs as a way of explaining "how to use it"

Additionally (if I should move this to a separate issue, let me know and I will do so) I would recommend an example specifically showing how to sha3::Keccak256::digest(b"a message") in one go. Finally, the example(s) that use update should add more than one message. This would be so that show new user why you would use new and then update rather than digest ("because you can add more than one thing").

I would be willing to create the examples / documentation if this would be agreeable

Start by reviewing the documentation for hasher state types such as sha3::Keccak256 and the existing examples using Digest::update. Add a reference to the Digest trait, show a one-shot Keccak256::digest example, and use multiple messages in incremental examples so the distinction is clear. The documentation is done when newcomers can understand both usage patterns.