Add missing imports in documentation

[jfmengels]

I've noticed a few missing imports in the examples.

A few notes: The imports are not sorted the way that elm-format sorts them. Would you like to see this be done as well?

I've only done it for this module, but I've seen some examples in Test.Html.Query where imports are missing and/or lead to confusion and invalid code. (See for instance Test.Html.Query.keep where text is used from both Html and Test.Html.Selector, and similarly Test.Html.Query.children uses class in the same invalid way). Let me know if you want me to solve this (and if so, indicate how you would prefer to see these collisions resolved). Maybe other modules have import issues, I haven't looked at it yet.

[Janiczek]

Thanks Jeroen!

The imports are not sorted the way that elm-format sorts them. Would you like to see this be done as well?

Yeah that would be nice!

[Janiczek]

Let's keep Test.Html.Query for some other day 👍

[Janiczek]

Your other PR #242 made this PR redundant - closing because there's nothing in the diff anymore :)