Rewrite the HPE NonStop Notes file in Markdown with more explanations.

Rewrite the HPE NonStop Notes file in Markdown with more explanations.

CLA: Permission is granted by the author to the OpenSSL team to use
these modifications.

Fixes #13237

Signed-off-by: Randall S. Becker <rsbecker@nexbridge.com>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13238)