feat: Simpler integration with the new setupFilesAfterEnv jest feature

[maraisr]

Off the back of what @kentcdodds is doing over at https://github.com/testing-library/jest-dom and its simple:

// jest.config.js

module.exports = {
   setupFilesAfterEnv: [
       require.resolve('jest-dom/extend-expect'),
   ],
}

I aim to introduce something similar to that, that would alleviate the need for a jest setup file.

Which will allow:

// jest.config.js

module.exports = {
   setupFilesAfterEnv: [
       require.resolve('snapshot-diff/extend-expect'),
   ],
}

Or this at the top of the spec file:

import 'snapshot-diff/extend-expect';

[thymikee]

Sure, why not. Thanks!

[thymikee]

Can you update the docs as well?