Add MLB Gameday API Primer

The MLB Gameday API Primer is a basic overview of the URL structure and
data organization. It is not meant to be an exhaustive description of
the API, rather it gives the reader enough information to get started
working with the data provided by MLB.
Add MLB Team Information Table

The MLB Team Information Table is meant to be a reference for all
information pertinent to MLB teams and used by the MLB Gameday API. It
includes team ID, team code, file code, team abbreviation, team name,
full name, and brief name data.