Update Contributing guide to say merging onto master is okay (#564)

CONTRIBUTING.md

@@ -80,7 +80,7 @@ npm run format
   - Good: `Fix dropped keystrokes on Firefox`
   - Bad: `Fix issue`
 - If your PR is not ready for review, mark it as "draft."
-- [Rebase your changes](https://www.atlassian.com/git/tutorials/rewriting-history/git-rebase) onto the latest `master` commit so that there are no merge conflicts.
+- Merge or [rebase](https://www.atlassian.com/git/tutorials/rewriting-history/git-rebase) your changes with the latest `master` commit so that there are no merge conflicts.
 - Your PR must pass build checks in CI before it will be considered for merge.
   - You'll see a green checkmark or red X next to your PR depending on whether your build passed or failed.
   - You are responsible for fixing formatting and tests to ensure that your code passes build checks in CI.