Add comment to resolv.conf when overwriting, mention what did it
In https://superuser.com/a/327358/660666 people discuss what is overwriting resolv.conf. And in https://wiki.debian.org/resolv.conf#Configuring_dhclient we see
The most common daemon which overwrites resolv.conf is dhclient(8) (from isc-dhcp-client).
OK that's great. But to reduce the mystery, I propose when overwriting, please also add a note to the file saying what package overwrote it.