get the cohort started with React Testing Library

[alodahl]

Please make any necessary changes to this cloned file so that it’s directions make it easy to understand some of the basics of React Testing Library, ideally in the context of a create-react-app: https://github.com/Techtonica/curriculum/blob/main/testing-and-tdd/react-testing-jest-and-RTL.md.
I left a few suggested links at the bottom of the file.

Note that this would come after https://github.com/Techtonica/curriculum/blob/main/testing-and-tdd/jest.md, so they have already had an intro to Jest. jest.md would be a good template for introducing RTL instead, so feel free to follow the pattern. The ultimate goal is that they have a foundation for adding RTL to their eventonica-react project the next day.

See #1608 for more context.