[User Story] Provide useful instructions for instructors post-installation

[jody]

Story

As an instructor,
I want simple, easy to follow, instructions for using ClassPoll after it's been installed,
So that I am more likely to use this tool rather than find it too cumbersome.

Acceptance Criteria

• Post-installation usage instructions exist targeting instructors
• Instructors rate this tool as easy-to-use in comparison with other tools like Mentimeter
• Instructions have an "at-a-glance" characteristic

[jody]

First step is to create USAGE.md

[jody]

Consider reworking the user experience so that there are fewer things that need explanation once the product has been fully set up.