If we follow the path we took in React Testing Library then that'll mean that people wont have to do anything fancy to make the typings/autocomplete show up which would be rad.

Specifically:

1. Add testing-library__jest-dom to DefinitelyTyped
2. Add @types/testing-library__jest-dom to @testing-library/jest-dom dependencies

I just tested it locally and that appears to work. If I have it in my node_modules then it just works™️

Anyone up for this?