As you may already know, Aurelia 2 is still in an early development phase. I guess that’s why the documentation for the new v2 release (https://docs.aurelia.io) is indeed not (yet) accessible from Aurelia’s main site.
The Aurelia 2 documentation is also available in its GitHub repository (https://github.com/aurelia/aurelia). I assume that the new documentation site is regularly (or even automatically) built from the GitHub repo.