Update NGINX Proxy Manager Documentation

[CorneliousJD]

https://vikunja.io/docs/reverse-proxy/#nginx-proxy-manager-npm

This doc is outdated.

You no longer have console into the container and edit the config, you can do it all via the GUI.

Here's an example -- can replace api with IP of the api service if it has one set.

[kolaente]

Would you mind sending a PR to fix it? I don't personally use NPM so I can't really add screenshots or other things for it.

Here's the file: https://github.com/go-vikunja/api/blob/main/docs/content/doc/setup/reverse-proxies.md

[CorneliousJD]

sure thing, done! I'll let you review and merge as you see fit :)