blake2b,blake2s: clarify difference between blake2b and blake2s
Fixes golang/go#37784
Run-TryBot: Katie Hockman
TryBot-Result: Gobot Gobot
// Package blake2s implements the BLAKE2s hash algorithm defined by RFC 7693
// and the extendable output function (XOF) BLAKE2Xs.
//
+// BLAKE2s is optimized for 8- to 32-bit platforms and produces digests of any
+// size between 1 and 32 bytes.
// For a detailed specification of BLAKE2s see https://blake2.net/blake2.pdf
// and for BLAKE2Xs see https://blake2.net/blake2x.pdf
//
