HOT guide structure

This patch provides a structure for the HOT guide, without content. The
intent is to provide an overview of what needs to be documented.

The organization will probably change once we turn this book into a
chapter in the user guide.

Change-Id: I640c519e2c0d1f1b6ba974f37aa4cb2abcfd59c1
Implements: blueprint heat-templates
Merge "HOT guide structure"