Container's IP required when proxying : add explanation text

[Anatharias]

Describe the bug

It's not a bug, it's a feature request: add one sentence, regarding containers IPs

While trying to get Portainer properly reverse proxyed, I spent quite a while figuring that since it's a docker container, the container IP or docker hostname was to be provided, and not the actual server IP.

A short extra sentence explaining this would be greatly appreciated by newcomers trying to get a docker container to accept one's login info.

Under the Target field:
This may be something like https://some.other.website/ (for explicit redirect) or http://127.0.0.1:1234/ for reverse-proxies. For a Docker container, provide it's IP instead of the server's IP

Context

• Hardware: Old laptop
• YunoHost version: 11.2.9.1
• I have access to my server: Through SSH | through the webadmin | direct access via keyboard / screen | ...
• Are you in a special context or did you perform some particular tweaking on your YunoHost instance?: yes
  • installed docker, then Portainer, following installation methods described in both their webpages
• Using, or trying to install package version/branch:
• If upgrading, current package version: can be found in the admin, or with yunohost app info $app_id

Steps to reproduce

Install docker : https://docs.docker.com/engine/install/debian/
Install Portainer : https://docs.portainer.io/start/install-ce/server/docker/linux
create a specific domain: portainer.local
create a redirect (using the server's IP and portainer port)

result: portainer landing page works, but the login isn't working.

Expected behavior

being able to log in with portainer credentials

Logs

no relevant log.
Though, loging in with the server IP in Nginx creates this error: Your session has expired

problem is solved when using the container IP as a proxy_pass and allowing visitors to access the redirection.

Thanks