[tor-relays] Reminder: exit nodes probably shouldn't be using Google's DNS servers

Hi, all! While looking into a bug report, I noticed that an exit node was using one of Google's well-known public DNS servers for its own DNS server. No disrespect to the operators of Google's fine public DNS service, but my sense is that using it for a Tor exit node might not be the greatest idea for users' privacy, having one DNS provider that gets to see so many requests. It's probably a better idea to have your own local cacheing DNS server. Would anybody like to share a guide about how to set one of those up safely and migrate correctly? best wishes, -- Nick