Improves docs a bit

[sobolevn]

1. Adds links to types that we are talking about
2. Adds .. code-block:: python in all places, otherwise this code was not highlighted on github

I really hope that RTD will build my PR to test it out, I am too lazy to test it locally 😆

[sobolevn]

Looks like it will 🎉

[sobolevn]

Looks like it won't 😞

[sobolevn]

Some unrelated updates:

• I am using phantom-types as an example of how one can work with my own project dry-python/classes, link: Concrete generics support dry-python/classes#24 (comment)
• I am also writting an article about phantom-types in my blog (https://sobolevn.me/), ETA is about one month: I will send you the link

Thanks a lot for your hard work! 👍

[antonagestam]

Thanks for the patch, it's first one for this package! 🎉

Hmm, seems like the coverage setup isn't working, I'll look into it!

[antonagestam]

Thanks for the patch @sobolevn! 🍰 I switched to something more conventional for coverage reports.