remi-realtime-db

Open port

When add new rdb server, please add and open its port.

Given the port need to open is 8090, the command is:

``bash
firewall-cmd --zone=public --add-port=8090/tcp --permanent
firewall-cmd --reload
``

ref: https://www.digitalocean.com/community/tutorials/opening-a-port-on-linux