Document "Getting Started" Environment for new developers

[ohessel]

This is related to the Dev Test Cluster work @razvan is doing

[lfrancke]

We now have the Dev Test Cluster but we need to add it to the documentation.

[lfrancke]

We will have a "Getting Started" section which is based on k3s (or other K8s distro) but I'd like to have a section for developers on how to set up a local (development) environment using kind or k3s (I don't really care) so that I can run a full distributed (more than one node) Stackable cluster on my local machine.

[lfrancke]

Refinement question: Is this already covered by #76
@razvan @Jimvin