Add instructions for running the app locally in production mode

[thenbe]

The docs make it clear how to run this app locally in "watch" mode.

It would be helpful if there were also instructions on how to run this app locally, but in a more optimized mode (commonly referred to as "production" or "preview" mode). Watch mode is great for when you're actively hacking on the code. But when you're serving the app over a network it creates unnecessary overhead.

I tried to npm run build in both the frontend/backend I kept facing issues after running the built files where the MAPS_API_KEY and GOOGLE_APPLICATION_CREDENTIALS were not being recognized (the credentials themselves are valid as they work fine when running in watch mode). Should I have used the docker(-compose) files instead?

My use case is that I want to build the app, run it locally, then serve it with a reverse proxy over an internal network.