Experiment with Direct Docker Image Deploy

If you don't have an image but would like to try out Direct Docker Image Deploy, here's an example:

1. Create a new App on Aptible. Note the handle you give to the App. Going forward in this article, we'll refer to it as $APP_HANDLE.
2. Use the aptible deploy command to deploy a public Docker image to your App:

aptible deploy --app "$APP_HANDLE" \
        --docker-image httpd:alpine