Add compute instance group data source (hashicorp#267)

Author: aadidenko

docs/d/google_compute_instance_group.html.markdown

@@ -0,0 +1,49 @@
+---
+layout: "google"
+page_title: "Google: google_compute_instance_group"
+sidebar_current: "docs-google-datasource-compute-instance-group"
+description: |-
+  Get a Compute Instance Group within GCE.
+---
+
+# google\_compute\_instance\_group
+
+Get a Compute Instance Group within GCE.
+For more information, see [the official documentation](https://cloud.google.com/compute/docs/instance-groups/#unmanaged_instance_groups)
+and [API](https://cloud.google.com/compute/docs/reference/latest/instanceGroups)
+
+```
+data "google_compute_instance_group" "all" {
+	name = "instance-group-name"
+	zone = "us-central1-a"
+}
+```
+
+## Argument Reference
+
+The following arguments are supported:
+
+* `name` - (Required) The name of the instance group.
+
+* `zone` - (Required) The zone of the instance group.
+
+- - -
+
+* `project` - (Optional) The project in which the resource belongs. If it
+    is not provided, the provider project is used.
+
+## Attributes Reference
+
+The following arguments are exported:
+
+* `description` - Textual description of the instance group.
+
+* `instances` - List of instances in the group.
+
+* `named_port` - List of named ports in the group. 
+
+* `network` - The URL of the network the instance group is in.
+
+* `self_link` - The URI of the resource.
+
+* `size` - The number of instances in the group.

google.erb

@@ -22,6 +22,9 @@
       <li<%= sidebar_current("docs-google-datasource-compute-zones") %>>
       <a href="/docs/providers/google/d/google_compute_zones.html">google_compute_zones</a>
       </li>
+      <li<%= sidebar_current("docs-google-datasource-compute-instance-group") %>>
+      <a href="/docs/providers/google/d/google_compute_instance_group.html">google_compute_instance_group</a>
+      </li>
       <li<%= sidebar_current("docs-google-datasource-container-versions") %>>
       <a href="/docs/providers/google/d/google_container_engine_versions.html">google_container_engine_versions</a>
       </li>