Add rel=sponsored to sponsor links

[ChristianMurphy]

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

Matching annotations to the ones used on https://unifiedjs.com/

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
mdx	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 12, 2024 7:58pm

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (908ff45) 100.00% compared to head (5eaf608) 100.00%.
Report is 7 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff            @@
##              main     #2439   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           23        23           
  Lines         2693      2694    +1     
  Branches         2         2           
=========================================
+ Hits          2693      2694    +1     

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[remcohaszing]

Since this is MDX, and not some markdown rendered on GitHub, perhaps we could leverage a React component. We could even avoid using a table altogether.

I approved, because I’m fine with this change regardless.

[wooorm]

This is copy/pasted from the readmes when everything is changed. That’s why it’s nice to have it similar to the rest, minimal changes.

I am not so worried about spam here: these are top doners who I am in contact with. Not random iffy betting things or so.

[wooorm]

Thanks!