issue #475: add doc about GKE node pools in terraform (#5289) (#3711)

Short explanation about why GKE node pools should be defined separately from the cluster resource
when using terraform.

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/5289.txt

@@ -0,0 +1,3 @@
+```release-note:note
+container: Added note about why node pools should be defined separately from the cluster
+```

google-beta/resource_compute_security_policy.go

@@ -10,7 +10,7 @@ import (
 	"github.com/hashicorp/errwrap"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/validation"
-	"google.golang.org/api/compute/v0.beta"
+	compute "google.golang.org/api/compute/v0.beta"
 )
 
 func resourceComputeSecurityPolicy() *schema.Resource {

google-beta/resource_gke_hub_feature_membership_test.go

@@ -5,7 +5,7 @@ import (
 	"fmt"
 	"testing"
 
-	"github.com/GoogleCloudPlatform/declarative-resource-client-library/dcl"
+	dcl "github.com/GoogleCloudPlatform/declarative-resource-client-library/dcl"
 	gkehub "github.com/GoogleCloudPlatform/declarative-resource-client-library/services/google/gkehub/beta"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/terraform"

website/docs/r/container_cluster.html.markdown

@@ -61,6 +61,10 @@ resource "google_container_node_pool" "primary_preemptible_nodes" {
 }
 ```
 
+~> **Note:** It is recommended that node pools be created and managed as separate resources as in the example above.
+This allows node pools to be added and removed without recreating the cluster.  Node pools defined directly in the
+`google_container_cluster` resource cannot be removed without re-creating the cluster.
+
 ## Example Usage - with the default node pool
 
 ```hcl