Docs: Document how to build and use locally.

[jefftriplett]

High level notes:

docker-compose --profile=docs up

Open http://localhost:4000

[jefftriplett]

I'm leaning towards a docker compose docs profile might be the easier option. Then everything stays in docker.

[saadmk11]

I think we should consider having both options because if someone just wants to contribute to the documentation they might not want to use docker for that.