Update docs to specify workaround for required field: (GoogleCloudPla…

…tform#11885)

Co-authored-by: Stephen Lewis (Burrows) <[email protected]>

mmv1/third_party/terraform/website/docs/r/container_cluster.html.markdown

@@ -1293,6 +1293,8 @@ Enables monitoring and attestation of the boot integrity of the instance. The at
 * `cpu_manager_policy` - (Optional) The CPU management policy on the node. See
 [K8S CPU Management Policies](https://kubernetes.io/docs/tasks/administer-cluster/cpu-management-policies/).
 One of `"none"` or `"static"`. If unset (or set to the empty string `""`), the API will treat the field as if set to "none".
+Prior to the 6.4.0 this field was marked as required. The workaround for the required field 
+is setting the empty string `""`, which will function identically to not setting this field.
 
 * `cpu_cfs_quota` - (Optional) If true, enables CPU CFS quota enforcement for
 containers that specify CPU limits.