bind-chroot mounts /var/named into the chroot so replace potentially misleading documentation.

This is necessary because otherwise there is an edge case where zones are
deployed directly after bind-chroot is installed (but not yet running) so when
named eventually starts, it won't bind mount /var/named onto
/var/named/chroot/var/named - resulting in errors because a whole bunch of
files are missing.

Tested on CentOS 5 and 6.
Update the README for RHEL 5.
Better phrasing.
Expand on the severity, e.g. it might break something if you don't be careful on RHEL6.
Make the wording a bit clearer, and case BIND correctly.
Merge pull request #18 from jaysh/master-chroot-documentation-changes

Suggestions to clarify documentation for bind-chroot