That’s a bit confusing, since what follows is a guide for installing and configuring nginx outside the container.
In any case, today I realized an additional benefit of this external nginx configuration: If you are used to seeing IP addresses 127.0.0.1 or your docker address (probably starting with 172.) as a registration or login IP address, it may have been because IPv6 traffic being forwarded into the container did not carry its IPv6 address along with it, unlike IPv4. With this configuration, you will now see correct IPv6 addresses instead of local addresses.
In other words, this configuration is essentially required for correct function of a useful administrative tool on the increasingly-IPv6 internet. (In the US, this includes lots of mobile traffic.)