On: Reasons to Prefer Blake3 over Sha256

[oconnor663]

We go over some of our reasoning around that in section 7.5 of https://github.com/BLAKE3-team/BLAKE3-specs/blob/master/blak.... An early BLAKE3 prototype actually didn't include the chunk counter (https://github.com/oconnor663/bao/blob/master/docs/spec_0.9....), so I'm definitely sympathetic to the use cases that wish it wasn't there. However, after publication we found out that something like a chunk counter is necessary for the security of the Bao streaming verification tool: https://github.com/oconnor663/bao/issues/41. It could be that there's a design that's the best of both worlds, but I'm not sure.