add snippet to readme to run prettier for all supported files

[tjenkinson]

Might be too much for the readme so feel free to close, but it's a snippet of code I wrote to automatically run all extensions prettier supports through prettier without having to keep a static list of extensions up to date.

[codecov]

Codecov Report

Merging #942 (1dbcb0a) into master (19d59fc) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #942   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           18        18           
  Lines          611       611           
  Branches       144       144           
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  Hits           611       611           

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[iiroj]

Looks good to me, even though it's getting pretty prettier-specific (pardon the pun).

If you feel like it, the README could use some collapsible sections for these examples:
https://gist.github.com/pierrejoubert73/902cc94d79424356a8d20be2b382e1ab

[tjenkinson]

Sounds good. Which ones should collapse? All of them?

[iiroj]

Yeah, let's collapse all the examples, and the examples in the JS config section (titles start with Example:).

[tjenkinson]

@iiroj done!

[github-actions]

🎉 This PR is included in version 10.5.4 🎉

The release is available on:

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

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