Missing mention of `BEHIND_PROXY` in reverse proxy setup

[jiriks74]

There's no mention of the need to set https://github.com/pelican-dev/panel/issues/2280 to true when using reverse proxy in the documentation:

Related: pelican/panel#2280

[mristau]

it is mentioned inside the compose-full-stack.yml which is the most current docker setup guide, the one inside docs is outdated

[parkervcp]

That's my bad. I've been busy with things and the main goal was fixes in the container and not docs right now.

I have more changes I need to make as well.

[jiriks74]

Understandable. I just got the error after an upgrade, but didn't find anything in the dost. Then I found the panel issue and tried using the search in docs in case I just missed it but it didn't return anything.

So I created an issue so that is wouldn't be forgotten about at the very least.

I'd look into making a PR but I'm braindead as it's too late right now and I have a lot on my plate this weekend. If it's still relevant when I have some time to spare on this I'll look into making a PR.