[FEATURE] Add Thumbs-Down Emoji to Contribution Guidelines

### Is your feature request related to a problem? Please describe.

Based on the discussion: https://lists.apache.org/thread/9bbbfjngvslv3sc1llo1sq6b0g97lvgq

I added this to my article on NuttX PRs: https://lupyuen.org/articles/pr#submit-the-pull-request

> __For PR Reviewers:__ Do NOT flag a PR or a Comment with the [__Thumbs-Down Emoji__](https://lists.apache.org/thread/9bbbfjngvslv3sc1llo1sq6b0g97lvgq). This is considered offensive in some cultures.

> Instead, mark the PR as "Request For Changes". And state precisely the changes needed for the PR.

Could someone help to add this to the NuttX Contribution Guidelines? Thanks!

Update: We could also include the ASF Generative Tooling Guidance, to help folks who are using LLMs and AI Tools: https://lupyuen.org/articles/pr#whats-next

> _Will NuttX accept Pull Requests generated with LLMs and AI Tools?_

> Check out the [__ASF Generative Tooling Guidance__](https://www.apache.org/legal/generative-tooling.html).

> _Why was my Pull Request rejected?_

> Some PRs are rejected because they're not consistent with the community guidelines. Refer to the following docs for guidance...

> - [__"NuttX Contributing Guidelines"__](https://github.com/apache/nuttx/blob/master/CONTRIBUTING.md)

> - [__"The Apache Way"__](https://www.apache.org/theapacheway/)

> - [__"ASF Project Independence"__](https://community.apache.org/projectIndependence.html)

### Describe the solution you'd like

Please see above.

### Describe alternatives you've considered

_No response_

### Verification

- [x] I have verified before submitting the report.