Better documentation for initial setup of the dev environment

[daemontus]

Right now, the README describes how to run the database, the backend and the frontend. However, it does not describe how to populate the database with models, or how to update it afterwards (plus I had a few issues with port settings).

In the final documentation, we should have instructions on how to setup everything. In particular:

• How to start/stop the database using docker.
• How to load data into the database and update it if necessary ("updating" the raw data can be just copying from the other github repository).
• How to check/setup the database connection: I had to set the DATABASE_URL environment variable with the correct URL, including user, password, port, and database. It would be good to just write this down somewhere in case someone not familiar with the project needs to run it locally.
• I had to change the port in frontend/src/services/base.ts to 3000 (instead of 3001). I'm guessing in the final version, this URL will probably be another environment variable? Or some kind of configuration option?
• How to start the dev server for backend and frontend.