docs: Update small README.md typo

[robwalkerco]

Please verify the following:

• [x] yarn build-and-test:local passes
• [x] I have added tests for any new features, if relevant
• [x] README.md (or relevant documentation) has been updated with your changes

Describe your PR

Just a tiny readme typo fix!

[morganick]

Thanks @robwalkerco!