Add Gen AI Note to Readme

[nabobalis]

Provide a general description of the issue or problem.

We want to roll this text out to all repos in their readmes:

Usage of Generative AI
======================

We expect authentic engagement in our community.
Be wary of posting output from Large Language Models or similar generative AI as comments on GitHub or any other platform, as such comments tend to be formulaic and low quality content.
If you use generative AI tools as an aid in developing code or documentation changes, ensure that you fully understand the proposed changes and can explain why they are the correct approach and an improvement to the current state.

[Diya910]

Can I add this to all repositories of sunpy?

[nabobalis]

If you can make the required changes to this repository, then yes. If you try to do it manually for each repository, then no.

[Diya910]

I can write a code to add same piece of code to all repositories at the specified location.

[nabobalis]

That code already exists, its this repository.

[Diya910]

Yes yes , I will add that in this repository only.