Add How to Read this Guide content

[brynrhodes]

Add a section to the home page that provides introductory material for what is included in this guide and how to read it. Note that the guide is organized based on pages for each recommendation, where each page includes: 1) Narrative content (L1), 2) A functional description (L2), and 3) Computable content (L3).

Also note that the guide is a "Content IG" as described in the CPG-on-FHIR Implementation Guide and provide a link there for further reading.