docs/167429: geli(8) needs to mention unencrypted /etc/fstab requirement for encrypted root

[eadler at FreeBSD.org]

Synopsis: geli(8) needs to mention unencrypted /etc/fstab requirement for encrypted root

Responsible-Changed-From-To: eadler->freebsd-doc
Responsible-Changed-By: eadler
Responsible-Changed-When: Sun Sep 2 03:09:17 UTC 2012
Responsible-Changed-Why: 
I won't be looking at this PR for a while and I need to clear some out
of my queue

http://www.freebsd.org/cgi/query-pr.cgi?pr=167429