Architecture documentation for KuD.

Adding the architecture documentation for KuD. Since KuD is an existing project in ONAP there is sufficient documentation for it available in the project's repo. 

Added the basic outline of the document and I added an additional link pointing to it in the ICN documentation 

https://github.com/onap/multicloud-k8s/blob/master/docs/kud_architecture.rst

https://github.com/onap/multicloud-k8s/blob/master/docs/bare_metal_provisioning.rst