Add warning to make sure port 53 is closed on router during Pi-Hole configuration

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Checklist

• This issue is not a duplicate, I've searched the Issue Tracker
• This issue is not a question, I'm aware that I can submit questions via Mastodon, Twitter, Email, Reddit or Matrix
• This issue is a content request, and not a bug report, feature request, or anything other

What are you missing or what could be improved?

When setting up Pi-Hole, users should check that it isn't port forwarding to port 53. There is no such warning on the website.

What is the solution you'd like to see?

Add warning in the Pi-Hole section. Users should make sure that port 53 on the router remains closed.

Do you have additional comments?

N/A