push docker image to dockerhub

[decarboxy]

trafficstars

Now that we have a dockerfile, we can push it somewhere. Dockerhub (https://hub.docker.com/) is probably a reasonable place since it's free for open source projects and the de facto standard. If someone can create a dockerhub account associated with this project and put the login info in a github secret it'd be really straightforward to make a CI pipeline that pushes a built image either on PR merge or tag, depending on how releases are handled.