spec: docs update
@@ -77,6 +77,8 @@ type ClusterSpec struct {
//
// The version must follow the [semver]( http://semver.org) format, for example "3.1.0".
// Only etcd released versions are supported: https://github.com/coreos/etcd/releases
+ //
+ // If version is not set, default is "3.1.0".
Version string `json:"version"`
// Paused is to pause the control of the operator for the etcd cluster.
