Add invoice for @wooorm

[wooorm]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

Hi! Here are some highlights of this month:

• finished the v2 website for mdx (https://v2.mdxjs.com) and released an RC
• added support for GFM footnotes throughout unified — was quite complex to reverse engineer and doing so I found several bugs there which I reported (https://github.com/github/cmark-gfm/issues?q=author%3Awooorm)
• started going through readmes to improve the documentation in unified — a recent example is Add improved docs remarkjs/remark-gfm#25
• also sent out a looong overdue update about what happened recently, which I want to do more frequently

For this month: continue with pushing better readmes, meanwhile reducing the number of open issues and perhaps cleaning some docs on processes (such as in this repo)