Update docs/dns.rst
Update docs/dns.rst

Co-Authored-By: hoellen <18290d0479417aabcaf211586c2a093503c94cbc@users.noreply.github.com>
kaiyou/freeposte.io,kaiyou/freeposte.io,kaiyou/freeposte.io,kaiyou/freeposte.io