Update Contribution Guide for new Changelog Format

[ofthedove]

Thank you for taking the time to work on a Pull Request. Your contribution is really appreciated! 🎉
Please don't delete any part of the template, since keeping the provided structure will help maintainers to review your work more rapidly.

Sections marked as * are required and need to be filled in.

Breaking change

No Breaking Change

Proposed change*

This PR updates the contribution guide now that the changelog is no longer at the bottom of each web docs file, but in a json file alongside the blueprint.

Related to PR #954

Checklist*

• I followed sections of the Contribution Guidelines relevant to changes I'm proposing.
• I properly tested proposed changes on my system and confirm that they are working as expected.
  • No testing, docs only
• I formatted files with Prettier using the command npm run format before submitting my Pull Request.
  • No code change

[github-actions]

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