samples/net/dns: Update README file

The DNS client sample application was updated to use IP addresses
from the prj_*.conf files. This patch updates the README file to
reflect those changes.

Change-Id: Ic72510be8da208aef19fb188560221e1c2386457
Signed-off-by: Flavio Santes <flavio.santes@intel.com>
1 file changed