title: Use Dockerhub with Git Submodules
body: <p>I try to get the auto build feature working for some private github repositories which also have private git submodules. I looked up the <a href="https://docs.docker.com/docker-hub/builds/#creating-an-automated-build" rel="nofollow">documentation</a> and tried to add the deployment key to the submodule but I got the error "Key is already in use" on GitHub. Then I found out that you can not use one deployment key for multiple github repositories.</p>
  
  <p>So any idea how to solve it? Is there any way to create multiple deployment keys on the dockerhub side?</p>
  
  <p>Thank you in advance and cheers,</p>
  
  <p>Simon</p>