Remind users to check firewall on first start

[Compositr]

I think the first start guide in the wiki could be improved by reminding users to check their firewall, if they cannot access the page, and also remind users to allow traffic from port 53.

I don't know if this is a common issue or if it's just me, but when I was installing Adguard Home on my Raspberry Pi, I wasted a lot of time debugging and checking syslog, just to find out that ufw was blocking requests to port 53, making the DNS unresponsive

[ainar-g]

Hello and thanks for the suggestion! We have now added a paragraph about firewalls to the First Start section.