Install instructions don't seem to be correct for bridge relay on new ubuntu instance 20.04

I've gone through the guide here: https://community.torproject.org/relay/setup/bridge/debian-ubuntu/

When I hit this step: systemctl enable --now tor@default

I'll get this:

The unit files have no installation config (WantedBy=, RequiredBy=, Also=,
Alias= settings in the [Install] section, and DefaultInstance= for template
units). This means they are not meant to be enabled using systemctl.
 
Possible reasons for having this kind of units are:
• A unit may be statically enabled by being symlinked from another unit's
  .wants/ or .requires/ directory.
• A unit's purpose may be to act as a helper for some other unit which has
  a requirement dependency on it.
• A unit may be started when needed via activation (socket, path, timer,
  D-Bus, udev, scripted systemctl call, ...).
• In case of template units, the unit is meant to be enabled with some
  instance name specified.

Job for tor@default.service failed because the control process exited with error code.
See "systemctl status tor@default.service" and "journalctl -xe" for details.

I'm using a generic Ubuntu 20.04 instance on EC2/AWS. Indeed the error message seems correct. It seems I need to manually edit: /lib/systemd/system/tor@default.service which is missing the [Install] section at the bottom.

After adding:

[Install]
WantedBy=multi-user.target

To the bottom of tor@default.service unit file, it fixes the issue of me running, systemctl enable --now tor@default.

But my main question is, should this unit file be manually updated? or is the install doc missing a step? or is something else going wrong?

Thanks!