DOC: tune: explain the origin of block size for ssl.cachesize

A user could eventually ask himself where those 200 bytes block size are
coming from. This patch tries to better explain the origin in case
people are curious or want to double check the reality.

Signed-off-by: William Dauchy <wdauchy@gmail.com>
(cherry picked from commit 9a4bbfe151b8db72ef4f353b5a1c5e1d60b20646)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
1 file changed