Get ready for user selected DNSs

Prep for using sed to insert user selected DNSs into 01-pihole.conf.
Selections will come from dialog during install script containing the
following choices: Google, DynDNS, and eventually 2 custom DNS servers.

advanced/01-pihole.conf

@@ -20,8 +20,8 @@ no-resolv
 
 # Add other name servers here, with domain specs if they are for
 # non-public domains.
-server=8.8.8.8
-server=8.8.4.4
+server=@DNS1@
+server=@DNS2@
 
 # If you want dnsmasq to listen for DHCP and DNS requests only on
 # specified interfaces (and the loopback) give the name of the