Documentation links on "Writing tests" does not link correctly

Created by: TryingToImprove

Is this a bug report?

Not sure

Environment

https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md#writing-tests

Steps to Reproduce

Click on "extensively documented here" or "jest.fn() and expect(fn).toBeCalled()"

Expected Behavior

Navigate to correct page. ....I am not sure where it should link to

Actual Behavior

Redirect to a 404