step one: tag the image so that it points to box bay!
$ docker image tag YOURCONTAINERNAMEHERE boxbay.hackclub.com/YOURIMAGENAME
step two: push it to the registry!
$ docker push boxbay.hackclub.com/YOURIMAGENAME
step three: pull it back from the registry to check that it worked, and then YOU'RE DONEEE
$ docker pull boxbay.hackclub.com/YOURIMAGENAME
YIPPEEE!! YOU JUST PUSHED YOUR FIRST CONTAINER TO BOX BAY!
now you have a link you can put in the form! (boxbay.hackclub.com/yourimagename)