Add a Note at bottom of Description

[nischaldutt]

Description

Added a Note at the bottom of description in Data Visualization with D3 Challenge.

Pre-Submission Checklist

• [x] Your pull request targets the dev branch.
• [ ] Branch starts with either fix/, feature/, or translate/ (e.g. fix/challenge-tests)
• [ ] All new and existing tests pass the command npm test.
• [ ] Use npm run commit to generate a conventional commit message. Learn more here: https://conventionalcommits.org/#why-use-conventional-commits
• [x] The changes were done locally on your machine and NOT GitHub web interface. If they were done on the web interface you have ensured that you are creating conventional commit messages.

Checklist:

• [x] Tested changes locally.
• [x] Addressed currently open issue

Closes #17767