Update pr checklist to remind updating the changelog

[maurolepore]

The changelog is becoming more important as our packages gradually gain more visibility -- to other developers as we increasingly collaborate, and to Deloitte team as we report our monthly progress during the dev-cycle meetings.

I edit the changelog with fledge but it's also easy to do manually:

• Edit NEWS.md
• Increment the version number in DESCRIPTION
• Tag the commit with the new version with something like:

git tag -a <version> -m "Some message"
git push origin <version>

---

TODO

• [ ] Link related issue/PR.
• [x] Describe the goal of the PR. Avoid details that are clear in the diff.
• [x] Mark the PR as draft.
• [ ] Include a unit test.
• [x] Review your own PR in "Files changed".
• [x] Ensure the PR branch is updated.
• [x] Ensure the checks pass.
• [x] Change the status from draft to ready.
• [x] Polish the PR title and description.
• [x] Assign a reviewer.

EXCEPTIONS

• [ ] Slide here any item that you intentionally choose to not do.