man: add security considerations to --compress section

man: add security considerations to --compress section

As Ahamed Nafeez reported to the OpenVPN security team, we did not
sufficiently inform our users about the risks of combining encryption
and compression.  This patch adds a "Security Considerations" paragraph
to the --compress section of the manpage to point the risks out to our
users.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1528020718-12721-1-git-send-email-steffan@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16919.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>