Documentation for packages

[Anber]

Linaria 3.0 introduces a dozen packages under the @linaria scope instead of the one linaria package. The problem here is that each package should have at least a short readme-file with a few words about the package and a link to the related documentation.

[jpnelson]

@Anber I'd be happy to help with this! I'll likely be upgrading our project to the v3 beta, I can help document along the way

[Anber]

@jpnelson it would be cool!