Clearify pointers to CKI documentation

The full guide is meant as an introduction, not something people should be digging through when trying to find out why they can't get CI to pass. Mark it as such, and point people to the FAQ for common operations such as failure debugging. The FAQ does cross link to other places when it's relevant so people don't need to guess when to look elsewhere.

Signed-off-by: Veronika Kabatova vkabatov@redhat.com