* Update README.md

Specify that serial must change for the zone file to be reloaded.
Signed-off-by: Grant Garrett-Grossman <grantlg2@illinois.edu>

* Update plugin/auto/README.md
Co-authored-by: Miek Gieben <miek@miek.nl>
Signed-off-by: Grant Garrett-Grossman <grantlg2@illinois.edu>
Co-authored-by: Miek Gieben <miek@miek.nl>