Update attached disk documentation (#3413)

<!-- This change is generated by MagicModules. -->
Original Author: @chrisst

website/docs/r/compute_attached_disk.html.markdown

@@ -22,6 +22,7 @@ To get more information about attaching disks, see:
 * How-to Guides
     * [Adding a persistent disk](https://cloud.google.com/compute/docs/disks/add-persistent-disk)
 
+**Note:** When using `compute_attached_disk` you **must** use `lifecycle.ignore_changes = ["attached_disk"]` on the `compute_instance` resource that has the disks attached. Otherwise the two resources will fight for control of the attached disk block.
 
 ## Example Usage
 ```hcl
@@ -29,6 +30,27 @@ resource "google_compute_attached_disk" "default" {
   disk = "${google_compute_disk.default.self_link}"
   instance = "${google_compute_instance.default.self_link}"
 }
+
+resource "google_compute_instance" "default" {
+  name         = "attached-disk-instance"
+  machine_type = "n1-standard-1"
+  zone         = "us-west1-a"
+
+
+  boot_disk {
+    initialize_params {
+      image = "debian-cloud/debian-9"
+    }
+  }
+
+  network_interface {
+    network = "default"
+  }
+
+  lifecycle {
+    ignore_changes = ["attached_disk"]
+  }
+}
 ```
 
 ## Argument Reference
@@ -77,7 +99,7 @@ The following arguments are supported:
   The mode in which to attach this disk, either READ_WRITE or
 	READ_ONLY. If not specified, the default is to attach the disk in
 	READ_WRITE mode.
-	
+
 	Possible values:
 	  "READ_ONLY"
 	  "READ_WRITE"