Add some prose to the documentation index page to guide readers to the
major manuals and guides.
Add a new "User Interaction Guide" to help the class of new user
who wishes to build a project with CMake for the first time, such as
after cloning a repo from a git repository.
Add a new "Using Dependencies Guide" to help the class of new
user who wishes to consume a SDK provided by a third party and needs a
starting point. This is a different type of user to the user who wishes
to create their own project from scratch (addressed by the
`cmake-buildsystem(7)` manual) as each will encounter needs for
information discovery in a different order.
