Inconsistent terminology for microk8s cloud

[sed-i]

I was trying to add-cloud a microk8s cloud, which led me through the following path:

• cloud doc: sounds like there are two kinds of substrates: a machine cloud and a k8s cloud. The cli commands are also contrasted there: add-cloud + add-credentials vs. add-k8s.
• The intro paragraph in the same cloud doc doesn't mention k8s clouds however. Need to read through the doc to realize it's possible to "add-cloud" (add-k8s, actually) a k8s cloud.
• In the MicroK8s doc, the terms "k8s cloud" and "microk8s cloud" are used interchangeably.
• MicroK8s is the one listed under "supported clouds", but there is no distinction between "machine clouds" and "k8s clouds", leading to believe that add-cloud can be used for microk8s.
• The add-k8s doc doesn't mention the "microk8s cloud".