Add info about default public images at docker hub

docs/configuration/docker-registry.md

@@ -8,6 +8,8 @@ title: Registry
 
 The default registry is Docker Hub, but you can change it using `registry/server`.
 
+By default, Docker Hub creates public repositories. To avoid making your images public, set up a private repository before deploying, or change the default repository privacy settings to private in your [Docker Hub settings](https://hub.docker.com/repository-settings/default-privacy).
+
 A reference to a secret (in this case, `DOCKER_REGISTRY_TOKEN`) will look up the secret
 in the local environment: