Just run docker-compose up -d, and you're okay. Your Unity container should be running when build is done.
There is a directory /context which is shared volume, so you can put your projects there.
By VNC, use your favorite VNC viewer and connect to 172.16.250.10 with pass123 as password. Also, you can change default password in docker-compose.yml, specified as environment variable VNC_PASSWORD.
Once you're connected run /opt/Unity/Editor/Unity and register/login with your UnityID credentials.
Of course, if you need bash for any reason just do docker exec -it unity-service bash.
Since Unity on Linux complains about running as root which is Docker's default, we have adminuser here who is also sudoer with no password. So if you need to do something you can either sudo something without password, or docker exec -it --username root bash and do stuff as root.
I specifically made this with unity-editor_amd64-5.6.0xf3Linux version because I needed it for one super-secret project. Unfortunately that version doesn't support activating via command line parameters. If you need that use version 2017.2 or later which has --username, --password and --serial parameters which allows you to streamline whatever you're up to.
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