There are two scenarios I can imagine in where you want to configure the DNS set by PiHole
1. You have multiple PiHole's in your LAN
2. You have a multi-layer DNS setup
In either case, we can utilize `dnsmasq` configurations in order to set the DNS option. You should already notice `01-pihole.conf` and `02-pihole-dhcp.conf` in `/etc/dnsmasq.d`, we'll need to create one that is numbered `03-*` or greater. I'll use `/etc/dnsmasq.d/03-dhcp-dns.conf` as my example.
To set the initial DNS server to be from the router.