Getting started page uses redis instead of MongoDB

[gedex]

Following docs are targeted for quickstart-go and quickstart-python

• https://docs.docker.com/docker-cloud/getting-started/deploy-app/10_provision_a_data_backend_for_your_service/
• https://docs.docker.com/docker-cloud/getting-started/deploy-app/12_data_management_with_volumes/

but doesn't tell anything about MongoDB for data persistence. For new comer, they need to jump to this repo and official MongoDB image.