docs: add explanation about kubelet failure to register on master nodes

[robszumski]

On a master node, the kubelet will attempt to post status to the API over and over again.

We should add a note that this isn't an issue and also explain why this happens.

[jerrykan]

Is there any way to suppress these messages (ie. stop the kubelet process from trying to update the node status), or are logging these errors actually desirable?

[aaronlevy]

There is an upstream proposal for better handling this workflow (kubernetes/kubernetes#14140 (comment)).

Essentially, we still want the node to register itself with the api, but only want it running static pods and not accepting work from api-server.

Until then, I don't believe there is a good way of specifically suppressing these messages.

[jerrykan]

OK, thanks for the info.

[joshix]

Closed by #128