Publish Docker images to public registry

DEVELOPER.md

@@ -90,11 +90,15 @@ curl http://localhost:8000/api/v1/status | jq .version
 
 ### Docker images
 
-Images are pushed to `docker.dcglab.co.uk/kb/engine` with tags:
+Images are pushed to `docker.dcglab.co.uk/public/kb/engine` with tags:
 
 - `engine-v2.0.6-nvidia` / `engine-v2.0.6-cpu` — versioned
 - `latest-nvidia` / `latest-cpu` — latest release
 
+The release script authenticates to the registry using the
+`DOCKER_DCGLAB_CI_USERNAME` and `DOCKER_DCGLAB_CI_PASSWORD` environment
+variables.
+
 Override the registry and org via environment variables:
 
 ```bash