Update the documentation.

Document the acceptable inputs everywhere that uses the function.

website/source/docs/providers/google/r/compute_disk.html.markdown

@@ -37,9 +37,11 @@ The following arguments are supported:
     encoded in [RFC 4648 base64](https://tools.ietf.org/html/rfc4648#section-4)
     to encrypt this disk.
 
-* `image` - (Optional) The image from which to initialize this disk. Either the
-    full URL, a contraction of the form "project/name", or just a name (in which
-    case the current project is used).
+* `image` - (Optional) The image from which to initialize this disk. This can be
+    one of: the image self_link, projects/{project}/global/images/{image},
+    projects/{project}/global/images/family/{family}, global/images/{image},
+    global/images/family/{family}, family/{family}, {project}/{family},
+    {project}/{image}, {family}, or {image}.
 
 * `project` - (Optional) The project in which the resource belongs. If it
     is not provided, the provider project is used.

website/source/docs/providers/google/r/compute_instance.html.markdown

@@ -117,12 +117,11 @@ the type is "local-ssd", in which case scratch must be true).
 * `disk` - The name of the existing disk (such as those managed by
     `google_compute_disk`) to attach.
 
-* `image` - The image from which to initialize this
-    disk. Either the full URL, a contraction of the form "project/name", the
-    name of a Google-supported
-    [image family](https://cloud.google.com/compute/docs/images#image_families),
-    or simple the name of an image or image family (in which case the current
-    project is used).
+* `image` - The image from which to initialize this disk. This can be
+    one of: the image self_link, projects/{project}/global/images/{image},
+    projects/{project}/global/images/family/{family}, global/images/{image},
+    global/images/family/{family}, family/{family}, {project}/{family},
+    {project}/{image}, {family}, or {image}.
 
 * `auto_delete` - (Optional) Whether or not the disk should be auto-deleted.
     This defaults to true. Leave true for local SSDs.

website/source/docs/providers/google/r/compute_instance_template.html.markdown

@@ -176,8 +176,12 @@ The `disk` block supports:
 * `disk_name` - (Optional) Name of the disk. When not provided, this defaults
     to the name of the instance.
 
-* `source_image` - (Required if source not set) The name of the image to base
-    this disk off of. Accepts same arguments as a [google_compute_instance image](https://www.terraform.io/docs/providers/google/r/compute_instance.html#image).
+* `source_image` - (Required if source not set) The image from which to
+    initialize this disk. This can be one of: the image self_link,
+    projects/{project}/global/images/{image},
+    projects/{project}/global/images/family/{family}, global/images/{image},
+    global/images/family/{family}, family/{family}, {project}/{family},
+    {project}/{image}, {family}, or {image}.
 
 * `interface` - (Optional) Specifies the disk interface to use for attaching
     this disk.