docker run image-name actually executes these two behind-the-scenes.
docker create image-name => container-id docker start -a container-id => output
docker create takes an image and creates a container from it. Running this command will return the id of the container.
docker start -a takes the id of a container and starts the container.
-a tells Docker to watch for output from the container to print the output to our terminal. If we exclude
-a, the only output we will see is the id of the container.