Add examples of permanent remove/replace of server node in DR section

[tbeets]

For DR section:

@jnmoyne

...nice to have a bit of a walkthrough/example of how to replace a bad node with another (so showing in something like nats stream report or nats stream info the 'replicas' section and explaining what the * or ! in front of the node name means, and then showing using peer-remove, and then the replacement node being started, etc...)