TODO:
* Do home-manager
* Look at for more inspiration github.com:nix-community/impermanence/pull/108
* Common files github.com:nix-community/impermanence/issues/10
* Useful config: github.com:chayleaf/dotfiles/blob/f77271b249e0c08368573c22a5c34f0737d3a766/system/modules/impermanence.nix
This needs to be configured through the "Nextcloud Office" app,
specifically the WOPI setting is important for security (I put both the
external IP, as well as `::1` and `127.0.0.1`).