point to docker install docs in our docker docs
For users who have heard that the using our Docker container is the easiest way to test the app, it's not clear from our current docs how you install Docker. Our current docs assume you have Docker already installed and working, which is fine, but we should call out to Docker's install docs at the top so people who don't already have it don't spend too much time trying to figure out how to run our Docker image without first setting up Docker.