Update readme to include fast fill logic

This #318 introduced a PrecreatingMode which actually let the CVO to push the clusterOperator in manifests.
This enables a new pattern for individual operators to set related objects into the clusterOperator defined in manifests/ openshift/cluster-kube-apiserver-operator#833
openshift/cluster-etcd-operator#312
openshift/cluster-kube-controller-manager-operator#398

Author: enxebre

docs/dev/clusteroperator.md

@@ -33,6 +33,11 @@ There are 2 important things that need to be set in the ClusterOperator Custom R
 - `.metadata.name`: name for finding the live instance
 - `.status.versions[name=operator].version`: this is the version that the operator is expected to report. ClusterVersionOperator only respects the `.status.conditions` from instances that report their version.
 
+Additionally you might choose to include some fundamental relatedObjects.
+The must-gather and insights operator depend on cluster operators and related objects in order to identify resources to create.
+Because cluster operators are delegated to the operator install and upgrade failures of new operators can fail to gather the requisite info if the cluster degrades before those steps.
+To mitigate this scenario the ClusterVersionOperator will do a best effort to fast-fill cluster-operators using the ClusterOperator Custom Resource in /manifests. 
+
 Example:
 
 For a cluster operator `my-cluster-operator`, that is reporting its status using a ClusterOperator instance named `my-cluster-operator`.