docs: update readme with changes in docs

[nickserv]

What:

Update readme with changes in docs

Why:

Most of the readme has been copied to the docs, but several changes in the docs haven't been copied back here yet

This is the first step of my work to move User Event documentation: testing-library/testing-library-docs#519 (comment)

How:

Reviewed all commits to docs (note that the file has been renamed from .md to .mdx) and copied them here

Checklist:

• Documentation
• Tests (N/A)
• Ready to be merged
  

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[codecov]

Codecov Report

Merging #701 (3b39a11) into main (a31ecc9) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main      #701   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           50        50           
  Lines          934       934           
  Branches       368       368           
=========================================
  Hits           934       934           

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[nickserv]

Note that this contains code from other contributors. I think it would be easier to move contributors around after the docs are moved, since most of this content would be deleted from User Event's readme anyway.

[github-actions]

🎉 This PR is included in version 13.2.1 🎉

The release is available on:

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

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