Better document URL routing rules

The inherited documentation from v1.x is out of date with the current implementation of BASE_PATH for the v2 ui. It currently uses environment variables like this:
`PUBLIC_PATH` defines the base url as viewed by the browser, on the external side of your ingress controller
`BASE_PATH` defines the url prefix with relation to the server instance, on the internal side of your ingress controller
`API_BASE_PATH` defines any prefix required before the /api/v2 proxy to gateway
`ASSETS` defines the location of your compiled assets, relative to the BASE_PATH, when hosted in production mode
`PORT` defines the port that the local server (nginx or webpack-dev-server) runs on

All together, replicating the v1 interface looks like:
`PORT=9999 PUBLIC_PATH=http://localhost:9999/yolo BASE_PATH=/yolo API_BASE_PATH=/yolo yarn start`

this issue is to add better configuration cascading to better replicate the v1.x implementation, while still keeping the flexibility, and to update the docs to reflect that change