Check on CI that docs.rs build is successfull

[hug-dev]

It's not ideal to make a release and hope for the best that the docs.rs build passes 😬
We should add on CI a way to check that the compilation works there. Maybe there is a Docker container that they use? Or someway to reproduce their environment.

[ionut-arm]

Yeah, it's annoying, I'll have a quick look - from what I remember, they have this massive local storage with all the crates and don't need to go over the network, and that would take a loooong time to build.

[ionut-arm]

They describe here how to check it locally. The first time around it'll take a while until it builds the environment, but after that it's going to be quick because everything is cached. You do need docker-compose, though! (and ~10GB of disk space)

I'll add this to the "publishing a crate" part of the book.