Content set configuration

Now we'll zoom into the AsciiDoc book level, and explore the V3 equivalent: content sets. At the book level, the system consists of:

System property	Asciidoc	V3
Content source files --> A whole bunch of markup files as well as any other assets used in the docs (for example, images, videos, and diagrams).	Markup: AsciiDoc files Assets: Images, videos, and diagrams	Markup: MD files Assets: Images, videos, and diagrams
Information architecture --> A way to specify the order in which these text-based files should appear in the information architecture of the book.	index.asciidoc file (this can be spread across several AsciiDoc files, but generally starts with the index file specified in the conf.yaml file))	TBD