Documentation should be more generalized for different platforms

Currently the getting started guide is specifically designed for users running Docker-for-mac. The docs should be generalized for many systems, such as windows, minikube, k3s, etc. (Thanks to @nabadger for brining this up)

@janhoy has given a great start to this with his training course: https://gist.github.com/4bc3398822b8b68ec94c60a05474e409

But it would be great if we could provide documentation that let you specify the system that you are using at the top and all examples would follow your system from then on. Don't think this is possible in markdown, but eventually it would be a great goal.

Start by reading the getting started guide and the linked training course to map which instructions currently assume Docker-for-Mac. A complete result would let readers identify their platform at the top and follow relevant examples for Windows, minikube, k3s, and other supported systems.

Written by the indexing model from the issue text.