add notes about having ccm and CNI installed

[kranurag7]

add a sentence that both CNI and CCM are required after the first control plane is ready, otherwise the cluster won't be usable.

Originally posted by @janiskemper in #252 (comment)

[guettli]

I would even like to automate that. If there is no CNI and no ccm, then there should be a Condition and an Event. I think a lot of potential new caph users fail here, because they are not familiar with the basics.

But that is perfectly fine. I have been there some months ago, too. An Event which points you in the right direction would help.

There is an open issue for creating an Event+Condition of fundamental things are missing: #1209