Add README.md and comment the code.

Dockerfile, docker-compose.yml: Use non-root user for celery. Fixes #1.

Etc: Add cryptopgrahy keys to make it easier to reproduce the example.

Make the app usable as a Celery worker.

Make the example more generic.

Move Cassandra initialisation out of the app.

Add JWT authentication.

Use Django REST instead of Flask.

Use Python 3.6.

Use string IDs and add aggregated feed.

Add follow and feed endpoints.

Initial commit with a version that seems to write activities to Cassandra.