Fix getting started on Eclipe Kapua website

[Coduz]

Describe the bug
We need to update informations on the Eclipse Kapua project website about getting started.

$ git clone git@github.com:eclipse/kapua.git kapua
$ cd kapua/deployment/docker
$ ./docker-deploy

This need to be fixed and also there is a not available image on the Kura section.

[lorthirk]

I fixed the Getting Started guide adding Git as a prerequisite, fixing the Unix script path and adding the Windows quickstart. As per the Kura image, it's not on the server anymore, so I removed the reference.