Update README.md (#4068)
Update README.md (#4068)

* Update README.md

Specify that serial must change for the zone file to be reloaded.

Signed-off-by: Grant Garrett-Grossman <fc4eb67f84809634880029e2e93dc40d17be855f@illinois.edu>

* Update plugin/auto/README.md

Co-authored-by: Miek Gieben <00b357f94cf3a1145a32703fb42e2d80418ab806@miek.nl>
Signed-off-by: Grant Garrett-Grossman <fc4eb67f84809634880029e2e93dc40d17be855f@illinois.edu>

Co-authored-by: Miek Gieben <00b357f94cf3a1145a32703fb42e2d80418ab806@miek.nl>
johnbelamaric/coredns,miekg/coredns,johnbelamaric/coredns,yongtang/coredns,miekg/coredns,chrisohaver/coredns,coredns/coredns