📝 Documentation: Mention what Tidelift does

[JoshuaKGoldberg]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Tidelift is a great thing but not everyone knows what it does. The docs here should mention it's a service that lets companies put money into a fund that gets distributed amongst their open source dependencies. Those dependencies need to show they do some good practices around maintenance & security in order to receive funds. It's a really good idea IMO - win win!

I'm wondering if I should put a (?) infotip/popover on the site too..

Additional Info

Thanks @matthew-dean for pointing out that this is never mentioned anywhere!

Sibling issue to JoshuaKGoldberg/tidelift-me-up#47.