Updating PR form to better explain release notes

[john-science]

What is the change?

The PR form was updated to better outline how the release notes should be used.

Why is the change being made?

We now have a "requirements" section in the release notes. And I think it would be helpful to include an "API changes" section.

---

Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in pyproject.toml.
• The release notes have been updated if necessary.

[opotowsky]

Looks good!