Tweak the organisation importer to log its activity

This branch changes the organisation importer so that it logs what it's doing. There's also a new section added to `README.md` to explain how to run the importer in the dev environment.

In the development environment, the importer will log to `STDOUT`. In the production environment, the importer will log to `log/organisation_import.log`, which we can consume in logstream so that we can see it in Kibana.