Document mDNSResponder -- corrupted stack crash when parsing bad resolv.conf

This only happens on a system where one has a system where
resolv.conf is writable by an untrusted user or where mdnsd is setuid
and can be tricked into opening an alternate resolv.conf.
PR: ports/147007
Submitted by: jmallett@
Approved by: tabthorpe (mentor)
Feature safe: yes