docs: XML documentation guidelines for sniffs (#2462)

[Nihakadiyam1]

This PR addresses issue #2462 by adding clear guidelines and examples for writing XML-style documentation in code sniff files:

• Usage of tags to highlight valid/invalid code
• Required indentation and line length

[rodrigoprimo]

Thanks for your willingness to contribute to this repository, @Nihakadiyam1.

This PR needs more work before it can be properly reviewed. A few guiding points that might help:

• The guidelines should be added to https://github.com/WordPress/WordPress-Coding-Standards/blob/01a76567f4aded1ecc432f23d03e597d3a91c9b2/.github/CONTRIBUTING.md instead of creating a new CONTRIBUTING.md file in the root of the repository.
• Have you checked the comments on #2462? They contain important suggestions on topics that should be covered in the guidelines, which I believe were not considered when creating this PR.

Please let me know if any of the above is not clear or if you need further help to move this PR forward.

[jrfnl]

@Nihakadiyam1 Thanks for you interest in contributing, but there is nothing in this PR which is usable. Feels like AI-slop, though I may be wrong.

I suggest closing this PR.