Update first_steps.md

too many issues with the setup, maybe adding a dedicated pointer to `HTTP_PORT=80` will help ...

docs/first_steps.md

@@ -17,7 +17,7 @@ This is just an example of how to obtain certificates with certbot. There are se
 wget https://dl.eff.org/certbot-auto -O /usr/local/sbin/certbot && chmod +x /usr/local/sbin/certbot
 ```
 
-2\. Make sure you set `HTTP_BIND=0.0.0.0` in `mailcow.conf` or setup a reverse proxy to enable connections to port 80. If you changed HTTP_BIND, then restart Nginx:
+2\. Make sure you set `HTTP_BIND=0.0.0.0` and `HTTP_PORT=80` in `mailcow.conf` or setup a reverse proxy to enable connections to port 80. If you changed HTTP_BIND, then restart Nginx:
 ``` bash
 docker-compose restart nginx-mailcow
 ```