Documentation: fix docker-compose.yml

[Mugane]

The documentation should wrap that docker-compose.yml file under services: like so:

services:
  nginx-ssl-proxy:
    image: danieldent/nginx-ssl-proxy
    restart: always
    environment:
      UPSTREAM: 127.0.0.1:8080
      SERVERNAME: test.example.com
      EXTRANAMES: www.test.example.com,test2.example.com
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - "/etc/letsencrypt"

If you don't, you'll get an error such as: (root) Additional property nginx-ssl-proxy is not allowed

Also, docker-compose up is deprecated, now it's docker compose up