[openssl/openssl] 04b538: Add design notes for XOF API.

[Shane]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: 04b53878ea498582a6c2cfa93c570584818bbe47
      https://github.com/openssl/openssl/commit/04b53878ea498582a6c2cfa93c570584818bbe47
  Author: slontis <shane.lontis at oracle.com>
  Date:   2023-11-02 (Thu, 02 Nov 2023)

  Changed paths:
    A doc/designs/xof.md

  Log Message:
  -----------
  Add design notes for XOF API.

Reviewed-by: Paul Dale <pauli at openssl.org>
Reviewed-by: Tomas Mraz <tomas at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21443)