Document how to use the fork+pull model with ADE
When working on a repository with a fork+pull model, it's not immediately obvious that ADE_IMAGES needs to be set to the container registry of the personal fork in order to fetch the Docker images.
When working on a repository with a fork+pull model, it's not immediately obvious that ADE_IMAGES needs to be set to the container registry of the personal fork in order to fetch the Docker images.