adds javascript comma first option to documentation

[andrewsuperlegit]

See my other pull request; js-beautify has an option for comma first formatting; so I added it to the readme and also here so people know about it :-)

What does this implement/fix? Explain your changes.

It literally just updates a readme to reflect a feature that js-beautify supports out of the box.
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Does this close any currently open issues?

No. But it would have if I had made an open issue- which I was going to do before I just did this myself.
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Any other comments?

pretty simple. literally just added to the readme and options
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Checklist

Check all those that are applicable and complete.

• [ x] Merged with latest master branch
• [ x] Regenerate documentation with npm run docs
• [ x] Add change details to CHANGELOG.md under "Next" section
• [ x] Added examples for testing to examples/ directory
• [ x] Travis CI passes (Mac support)
• [ x] AppVeyor passes (Windows support)