In order to run this image do:
docker-compose up -d to get all up.
On first run DB initialization and initial user setup is done like so:
First start a bash in the container:
docker-compose exec sentry /bin/bash.
Then, inside bash, do
sentry upgrade wait until it asks you for an inital user.
exit the bash.
When in doubt check with
docker-compose ps if all went fine.