Add reverse proxy guide

[MichaIng]

For all webservers, e.g. to enable HTTPS and simplified remote access: https://dietpi.com/phpbb/viewtopic.php?p=32945#p32945

[StephanStS]

I propose to describe the Nginx Proxy Manager.

See

• https://nginxproxymanager.com/
• https://blog.login.gmbh/nginx-proxy-manager-auf-dem-raspberry-pi-installieren/
• https://www.youtube.com/watch?v=h1a4u72o-64