Note VPN interference with door code system

[brittag]

What github issue is this PR for, if any?

None

What does this code do, and why?

Let people know that if they're on a VPN or iCloud Private Relay, the door code system may not work for them. This should help reduce confusion and inconvenience for people, because it's easy to resolve if you know what the issue is.

How is this code tested?

I don't know of any tests for this

Are any database migrations required by this change?

No

Are there any configuration or environment changes needed?

No

Screenshots please :)

I don't have any