Add machine type and min/max nodes flags to cluster creation command

A machine with more CPUs than default is required to meet the requirements
of some pods. A minimum of 3 nodes is required.

k8s/trillian/README.md

@@ -90,7 +90,9 @@ Create a new cluster from the command line:
 export CLUSTER=trillian-cluster
 export ZONE=us-west1-a
 
-gcloud container clusters create "$CLUSTER" --zone "$ZONE" --enable-autoscaling
+gcloud container clusters create "$CLUSTER" \
+  --zone "$ZONE" --machine-type=n1-standard-2 \
+  --enable-autoscaling --min-nodes=3 --max-nodes=10
 ```
 
 Configure `kubectl` to connect to the new cluster.