[openssl/tools] b6c908: Add how to handle security issues document

[Pauli]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/tools
  Commit: b6c9089c4ccf27e58a94ab677924fd5847b3bdcd
      https://github.com/openssl/tools/commit/b6c9089c4ccf27e58a94ab677924fd5847b3bdcd
  Author: Pauli <pauli at openssl.org>
  Date:   2023-08-10 (Thu, 10 Aug 2023)

  Changed paths:
    A HOWTO-handle-security-issue.md

  Log Message:
  -----------
  Add how to handle security issues document

Reviewed-by: Matt Caswell <matt at openssl.org>
(Merged from https://github.com/openssl/tools/pull/165)