GitLab CI/CD - Providing your own docker runners 

This is a very quick walkthrough to show how to configure a custom runner for GitLab CICD. It is based on Docker, and for convenience, we will use Play with Docker to execute our runner. If you know how to run docker in your own laptop, or in a cloud instance, do it there instead.
AGAIN: If you use PlayWithDocker to execute your containers, AVOID SHARING ANY SENSIBLE INFORMATION with your runner. Ideally, don't use it unless you create a throw-away GitLab account only for learning.