docs: Update setup to include import statement

[edmundsj]

I spent an hour trying to figure out what was wrong with my code, not realizing that user-events was an unnamed export. Please put an import statement somewhere in the docs, if not here, to save poor idiots like myself.

[netlify]

✅ Deploy Preview for testing-library ready!

Name	Link
🔨 Latest commit	82521a5
🔍 Latest deploy log	https://app.netlify.com/sites/testing-library/deploys/633df658a8a7860009653713
😎 Deploy Preview	https://deploy-preview-1153--testing-library.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[eps1lon]

Thanks!

[eps1lon]

@all-contributors Add @edmundsj for docs

[allcontributors]

@eps1lon

I've put up a pull request to add @edmundsj! 🎉

[ph-fritsche]

I think it's odd to include the import specifically in this paragraph.
If it isn't obvious by the declarations, we should add it in intro and/or install like #1143.
(Are there really IDEs that don't display the types we deliver with the package?)