Updated the instructions to free up port 53 in Fedora

[OptimoSupreme]

Description

1. Added a dedicated Fedora section below Ubuntu's since the Ubuntu instructions no longer work on Fedora.
2. Added 'Debian' to the title of the Ubuntu section since it is applicable there as well.
3. Fixed the heading level for Ubuntu to match the rest of the readme.

Motivation and Context

This provides Fedora Pihole user with accurate instructions on how to free port 53, which they do not currently have.
Existing Issue.

How Has This Been Tested?

This does not affect any other project code. I have verified that the included commands work as expected on a Fedora 41 server.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[yubiuser]

I think, both sections (Debian/Fedora) should go to https://docs.pi-hole.net/main/prerequisites/

instead. This is not a docker-specific configuration step, but affects bare metal the same way

[rdwebdesign]

I think, both sections (Debian/Fedora) should go to https://docs.pi-hole.net/main/prerequisites/

I agree.
This README is too long and contains too many details, but not all are directly related to docker.

Maybe the best approach would be to put these 3 items under "Tips and Tricks" with links to external pages:

but we first need to create the pages for the first 2 items in https://docs.pi-hole.net.