update docker run command in readme

update the volumes like so:

docker run \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -v /tmp/codalab-v2:/tmp/codalab-v2 \
    -d \
    --env BROKER_URL=amqp://rxvhdryk:cXPl4TnrDK-u56cZKGifTeWZGaDk0FWD@owl.rmq.cloudamqp.com/rxvhdryk \
    --restart unless-stopped \
    --log-opt max-size=50m \
    --log-opt max-file=3 \
    codalab/competitions-v2-compute-worker:latest