message: feat(dev): Add changelog instructions to `CONTRIBUTING.md`
  This adds instructions for updating the changelog, partially to ensure consistency and partially as a place to write down the relevant `git log` command and linkifying regex.
diff: @@ -79,7 +79,19 @@ When contributing to the codebase, please note:
  _These steps are only relevant to Sentry employees when preparing and publishing a new SDK release._
  1. Determine what version will be released (we use [semver](https://semver.org)).
  -2. Update [`CHANGELOG.md`](https://github.com/getsentry/sentry-javascript/edit/master/CHANGELOG.md) to add an entry for the next release number and a list of changes since the last release.
  +2. Update [`CHANGELOG.md`](https://github.com/getsentry/sentry-javascript/edit/master/CHANGELOG.md) to add an entry for the next release number and a list of changes since the last release. (See details below.)
  3. Run the [Prepare Release](https://github.com/getsentry/sentry-javascript/actions/workflows/release.yml) workflow.
  4. A new issue should appear in https://github.com/getsentry/publish/issues.
  5. Ask a member of the [@getsentry/releases team](https://github.com/orgs/getsentry/teams/releases/members) to approve the release.
  +
  +### Updating the Changelog
  +
  +1. Create a new branch.
  +2. Run `git log --format="- %s"` and copy everything since the last release.
  +3. Create a new section in the changelog, deciding based on the changes whether it should be a minor bump or a patch release.
  +4. Paste in the logs you copied earlier.
  +5. Delete any which aren't user-facing changes.
  +6. Alphabetize the rest.
  +7. Run a regex find and replace, searching for `\(#(\d+)\)` and replacing it with `([#$1](https://github.com/getsentry/sentry-javascript/pull/$1))`. (This will linkify all of the PR references.)
  +8. If any of the PRs are from external contributors, include underneath the commits `Work in this release contributed by <list of external contributors' GitHub usernames>. Thank you for your contributions!`. If there's only one external PR, don't forget to remove the final `s`. If there are three or more, use an Oxford comma. (It's in the Sentry styleguide!)
  +9. Commit, push, and open a PR with the title `meta: Update changelog for <fill in relevant version here>`.
  