The documentation is now live at reactnavigation.org, and v3 lives here.
In this release, we have removed the navigators from the react-navigation package. The navigators have lived in separate packages for quite a while and you could already use those packages manually, but we still bundled them in the react-navigation package. This made it difficult for us to release significant updates to navigators, because we had to then do a major version release of react-navigation too. By separating the navigator packages there is more freedom to update and improve navigators without any impact on folks that don't use them.