Initialize Glossary/Directory of core concepts in Cobalt

[TechnicallyWilliams]

Description

As a user I'd like a central page that lists all the core concepts of Cobalt.

Acceptance Criteria

Reference: [Done-Done Checklist] (https://github.com/Microsoft/code-with-engineering-playbook/blob/master/Engineering/BestPractices/DoneDone.md)

• List should be alphabetical
• Document should live in the Docs directory
• Each existing section of the Walkthrough should include at least one link back to the Core Concepts Doc

Tasks

• Visit each existing section of the Walkthrough and include at least one link back to the Core Concepts Doc