README: Add render options Example for container

[duncanleung]

Aside: Thank you for this library! I really really enjoy the API and testing philosophy behind it. Also, I really enjoyed your "Testing React Applications" workshop on Front End Masters!

I'm still very new to testing, so I hope that my README example makes sense. Open to all feedback! Thank you!

What:
README: Add render options example for container.

Why:
I was unit testing a tablebody element, and got a validateDOMNesting error because:

By default, react-testing-library will create a div and append that div to the document.body and this is where your react component will be rendered.

Warning: validateDOMNesting(...): <tbody> cannot appear as a child of <div>.
    in tbody (created by TableBody)
    in TableBody (created by TableBody)
    in TableBody

It was not straight forward for me to find out how to use the options parameter in the render() method.

I think it will be helpful to add an example to the README.

How:
My original unit-test was:

import React from "react";
import { render, cleanup, fireEvent } from "react-testing-library";

import TableBody from "../TableBody";
import listingDataMock from "../__mocks__/TableBody-listing-data";

afterEach(cleanup);

describe("TableBody", () => {
  test("Snapshot", () => {
    //Arrange--------------
    const listingData = listingDataMock;
    const tableBodyKey = "candidateId";

    const props = {
      listingData,
      tableBodyKey
    };

    const { container } = render(<TableBody {...props} />);

    //Assert---------------
    expect(container).toMatchSnapshot();
  });
});

Checklist:

• Documentation
• Tests
• Ready to be merged
  
• Added myself to contributors table
  

[kentcdodds]

This is great. Thanks!

[kentcdodds]

Would you like to add yourself to the contributors table?

[duncanleung]

Sure! Thank you!

I guess I have to do this with another PR since this one is merged already?

_{Sent with GitHawk}

[kentcdodds]

Yep 👍

[kentcdodds]

🎉 This PR is included in version 4.1.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀