Add a "call out" in the installation guide about the requirement to have all three nodes (Worker, Etcd, Controller)

[gunamata]

Feedback from customer:

“Rancher install documentation needs an update: The initial cluster requires you to have all three nodes (Worker, Etcd, Controller) installed for your first spin-up. If you fail to include one of the three, there is no message to let you know that it's waiting for one of them, and it does not fail nor prompt you. This should be called out in the docs. “

[martyav]

@gunamata Is there an associated ticket with more details on the user's setup? It's not clear to me what they mean by "initial cluster" -- on first impression, I thought the cluster Rancher server is on, but Rancher server can be installed on a single node.

[gunamata]

@martyav , It was a question on one of the Slack channels that I am not able to track down now nor able to recall the full context. I should have pasted the link to the thread here. :(