Docs - Emphasize which typeclasses/datatypes are most important to learn

Cats documentation lists a lot of typeclasses and datatypes. But for a newcomer, it's not clear which typeclasses/datatypes are the most useful/important.

For example OptionT is way more useful than Writer, but just looking at the docs, that's not clear at all. (You have to go to Discord for someone to point out to you that you will ~never use Write 🙂)

My proposal is to somehow emphasize the more important stuff and deemphasize the less important.

I also leave here feedback by @jducoeur:

"Important" is pretty subjective, so I'd be careful about phrasing, but it's certainly true that in my current class on Cats et al, there are a handful of typeclasses and data types I'm emphasizing, and leaving most of the rest for folks to look into if and when they need them.

Start with the linked Cats typeclasses and datatypes documentation pages, then review the issue's Discord feedback about subjective importance. The scope needs agreement on how to present priorities without overstating them; done would mean the documentation clearly guides newcomers toward the most useful material.