Rewrite guide to improve clarity, flow, markup, and consistency.

The rewrite includes:
Explicit commands for important options.
Use of lists to improve the clarity of the configuration variables content.
Removal of command prompts to enable DBT.
Consistent use of terminology.
Use of concrete examples to improve the clarity of the commands.
Improved content flow and navigation with linked workflow overviews.
Added cross-references.
Removed ambiguous relative pronouns and punctuation.
Removed passive voice whenever possible.
Changed verbs to present tense for consistency and style guide compliance.
Optimized headings for search engines.

Signed-off-by: Rodrigo Caballero <rodrigo.caballero.abraham@intel.com>