Improve the docs pages
https://huggingface.slack.com/archives/C0311GZ7R6K/p1663216598353539

> as discussed, lets' make https://huggingface.co/docs/datasets-server/index a little bit prettier because right now it's not very pretty – also the order of the sections is weird, no? Should be API basics (endpoint etc) > Valid datasets > Splits > First rows, no?
<img width="387" alt="image" src="https://user-images.githubusercontent.com/1676121/190364542-d5f820aa-300b-4533-a82b-f904969b78cb.png">

Improve the docs pages: https://huggingface.slack.com/archives/C0311GZ7R6K/p1663216598353539

> as discussed, lets' make https://huggingface.co/docs/datasets-server/index a little bit prettier because right now it's not very pretty – also the order of the sections is weird, no? Should be API basics (endpoint etc) > Valid datasets > Splits > First rows, no?
<img width="387" alt="image" src="https://user-images.githubusercontent.com/1676121/190364542-d5f820aa-300b-4533-a82b-f904969b78cb.png">
