message: add more notes around consuming a private registry image
diff: @@ -277,3 +277,20 @@ private-registries:
  password: MY_OWN_REGISTRY_PASSWORD
  url: my.own.registry.com
  ```
  +
  +To consume an image from a private registry, it needs to be used as the `FROM` in a `Dockerfile.<service>`
  +
  +```
  +#Dockerfile.mariadb
  +FROM dockerhubuser/my-private-database:tag
  +```
  +
  +And the service updated to use build instead of image
  +
  +```
  +services:
  + mariadb:
  + build:
  + context: .
  + dockerfile: Dockerfile.mariadb
  +```
  \ No newline at end of file
  