Add missing import in docs (testing-library#776)

Author: gangsthub

docs/queries/about.mdx

@@ -36,7 +36,7 @@ retries and the default testID attribute.
 ## Example
 
 ```jsx
-import { screen } from '@testing-library/react' // (or /dom, /vue, ...)
+import { render, screen } from '@testing-library/react' // (or /dom, /vue, ...)
 
 test('should show login form', () => {
  render(<Login />)