[docs] [issue21649] Mention "Recommendations for Secure Use of TLS and DTLS"

[Roundup Robot]

Changes by Roundup Robot <devnull at psf.upfronthosting.co.za>:


----------
pull_requests: +3405

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21649>
_______________________________________