Update README.md to fix spelling error

[derekbassett]

Description of the change: Fixes a small error in the README.md documentation.

Motivation for the change: To make sure the documentation is correct.

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• [ ] Add a new changelog fragment in changelog/fragments (see changelog/fragments/00-template.yaml)
• [ ] Add or update relevant sections of the docs website in website/content/en/docs