Implement environment file configs (and update documentation)

[jaydonkrooss]

In its current state, the app is in need of a way to extract environment variables set by developers when needed for integrations like Zoom, Twilio, and BlueJeans. Currently, running the app locally can only be done without these settings.

Make sure to reference a .env file in the Docker build (like how we have it on other projects such as MyLA). The Readme instructions ought to be updated to account for the user to create their own .env file as well.

Dev Test plan: try to add credentials for an integration using .env file (Twilio would probably be the easiest to check). And verify the integration is functional.