Update dockerizing.md

fix typo
Merge pull request #6718 from mchelen/patch-1

Update dockerizing.md
Relax dns search to accept empty domain

In that case /etc/resolv.conf will be generated with no search
option.

Docker-DCO-1.1-Signed-off-by: Fabio Falci <fabiofalci@gmail.com> (github: fabiofalci)