Improve README.md + QuickStart

[leowmjw]

README.md needs to be improved; some questions I had trying to get it running the first time:

• How to run the service in dev mode
• How to confirm that dev mode is working correctly
• How to connect it to the new popit_ng backend
• How to run the service in production; e.g what settings to be set

[sweemeng]

• server is run in dev mode essentially by running python server.py
• Currently server is defined in provider.py hardcoded. Need to refactor that to able to point to another popit_ng instance.
• also user is hard coded for now.
• There is no specific dev mode. The original idea is, this app should be replaced by a proper js one. This app will be development while still in used. It is meant to be an inhouse tool anway