[keycloak-dev] Docs ready again

[Stian Thorgersen]

Docs are now ready for changes again after the recent restructuring. It's
now all pure AsciiDoctor and we will no longer use GitBook.

Check out the README.md in the repo for instructions on how to build:
https://github.com/keycloak/keycloak-documentation/blob/master/README.md

Editing the docs is pretty much the same as before, but you don't need to
do the hacks with links and images anymore. All features from asciidoctor
should now work as well.