doc: clarify setcrypt defaults

Reviewed-on: http://gerrit.openafs.org/10111
Reviewed-by: Jason Edgecombe <jason@rampaginggeek.com>
Reviewed-by: Michael Laß <lass@mail.uni-paderborn.de>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 3a24ed9baef178d34b6d0fb3a5f6a485dea9353b)

Change-Id: I2d9cd3c9167e2d67ced609e5be2d173a82b36a28
Reviewed-on: http://gerrit.openafs.org/10136
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>