Update 6.0 guide

Author: zli82016

mmv1/third_party/terraform/website/docs/guides/version_6_upgrade.html.markdown

@@ -213,7 +213,7 @@ Previously `lifecycle_rule.condition.age` attirbute was being set zero value by
 Now `lifecycle_rule.condition.no_age` is no longer supported and `lifecycle_rule.condition.age` won't set a zero value by default.
 Removed in favor of the field `lifecycle_rule.condition.send_age_if_zero` which can be used to set zero value for `lifecycle_rule.condition.age` attribute. 
 
-For a seamless update, if your state today uses `no_age=true`, update it to remove `no_age` and set `send_age_if_zero=false`. If you do not use `no_age=true`, you will need to add `send_age_if_zero=true` to your state to avoid any changes after updating to 6.0.0.
+For a seamless update, if your state today uses `no_age=true`, update it to remove `no_age` and set `send_age_if_zero=false`. If you do not use `no_age=true`, you will need to add `send_age_if_zero=true` to your state to avoid any changes after updating to 6.0.0. 
 
 ## Resource: `google_container_cluster`
 
@@ -226,6 +226,15 @@ on the resource through Terraform and the default labels configured on the provi
 * The new output-only `effective_labels` field lists all of labels present on the resource
 in GCP, including the labels configured through Terraform, the system, and other clients.
 
+## Data source: `google_container_cluster`
+
+### Three label-related fields are now present
+
+All three of `resource_labels`, `effective_labels` and `terraform_labels` will now be present.
+All of these three fields include all of the labels present on the resource in GCP including
+the labels configured through Terraform, the system, and other clients, equivalent to
+`effective_labels` on the resource.
+
 ## Resource: `google_edgenetwork_network`
 
 ### Three label-related fields are now present