Add maintainers section to README

[jeffpaul]

What?

This PR lists maintainers in the readme and references the new maintainer team in order to ping the entire group (e.g. for PR reviews).

Copilot summary

This pull request updates the README.md to clarify and highlight the maintainers of the AI plugin repository.

Documentation improvements:

• Added a new section listing the current maintainers, including their GitHub handles and a link to the maintainers team for contact purposes.
• Clarified that the CREDITS.md file contains the full list of maintainers, contributors, and libraries.

Why?

How?

Use of AI Tools

Testing Instructions

Screenshots or screencast

Before	After

Changelog Entry

Developer - Add @WordPress/ai-maintainers team.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.68%. Comparing base (b4fb466) to head (78bb0ca).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #677   +/-   ##
==========================================
  Coverage      74.68%   74.68%           
  Complexity      1754     1754           
==========================================
  Files             85       85           
  Lines           7549     7549           
==========================================
  Hits            5638     5638           
  Misses          1911     1911           

Flag	Coverage Δ
unit	74.68% <ø> (ø)

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