Ok I have some. 
This is incomplete, needs the second path.
It should also happen before starting the service.
This should also happen before the service.
It is not required to use systemd-resolved but its main use is to provide backwards compatibility with resolvconf/openresolv … this may be pertinent for various VPNs and other considerations.
(provides symlink for /usr/bin/resolvconf)
Is sudo necessary here? Shouldnt polkit be allowed to handle the permission?
…
sudo pacman -Syu systemd-resolvconf
sudo cp /etc/resolv.conf /etc/resolv.conf.bak
sudo ln -sf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
systemctl enable --now systemd-resolved
sudo pacman -Rns openresolv
Its been a minute since I did a replacement so I dont recall if restarting NetworkManager or similar would be required. Of course a system reboot would be sure.
Some other info (like using FallbackDNS) are illustrated in some other posts but this bigger one comes to mind;
Oh, and I also am reminded that openvpn-update-systemd-resolved AUR package is handy for anyone using an openvpn connection.
(Pretty much does seamless switching of some tech such as DNS servers before/after VPN connection)