Copy in waitForElement docs

[alexkrolick]

What:

Why:

How:

Checklist:

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

[kentcdodds]

Thanks! I don't think we need more than just an example and a link to the docs in dom-testing-library.

[alexkrolick]

Changed it to just type signature + link

[kentcdodds]

Let's just add a simple usage example. 90% of people will understand how to use it from that, the other 10% can look at the dom-testing-library docs.

[kentcdodds]

Coolio! Thanks!