Create a guidance document for CORE

[OGarcia11]

https://cdisc.sharepoint.com/:w:/r/sites/CORERoadmap/_layouts/15/Doc.aspx?sourcedoc=%7B33024CAA-18AC-4D2E-8946-A51CE1E9E3A3%7D&file=CORE_Reference_Guide.docx&action=default&mobileredirect=true