Document the use of environment variable for production builds

[devraj]

The web has odd approaches for using a different set of environment variables for production builds. This is particularly important if you are using third part services like Stripe.

The task at hand is to explore what is the optimal way to provide environment variables for various environment, considering:

• CI/CD pipeline for building the front end apps
• Potentially being run on Github actions
• Avoid adding additional tooling to achieve management of environment vars