title: creating a directory using docker swarm compose/yaml file
body: <p>Is there a way to create a directory on the local file system via yaml file if it does not exist? 
  I currently am mounting a dir from my local file sys inside the container and it works. But if the dir on the file system does not exist, container launch fails as the dir cannot be mounted. How can I make this as seamless as possible and embed the dir creation logic in the swarm yaml file?</p>