Adapt Example Nginx Configuration

The current nginx example configuration in develop includes some parts I'm not missing in "my" ;) default debian nginx enviroment. But I miss the server_name parameter.

As example I would remove the map and default_site parts and add the server_name:

server {
  listen 80;
  listen [::]:80;

  server_name thekno.example.org;
  root /usr/share/thekno/html;

  set $origin_trial "";

  include /etc/nginx/snippets/thekno-spa.conf;
}

Im not sure about the docker-stuff, but I think it would be a good move to adapt this file running with both just changing server_name and port. Or we add a separate file just as debian default. Or I just don't get it, then I would document it :) @kmohrf what's the deal with the 'map' in the current file?