Add folder data source (hashicorp#738)

docs/d/datasource_folder.html.markdown

@@ -0,0 +1,39 @@
+---
+layout: "google"
+page_title: "Google: google_active_folder"
+sidebar_current: "docs-google-datasource-folder"
+description: |-
+  Get a folder within GCP.
+---
+
+# google\_active\_folder
+
+Get a folder within GCP by `display_name` and `parent`.
+
+## Example Usage
+
+```tf
+resource "google_folder" "new-folder" {
+  display_name = "new-folder"
+  parent = "folders/some-folder-id"
+}
+
+data "google_active_folder" "new-folder" {
+  display_name = "${google_folder.new-folder.display_name}"
+  parent = "${google_folder.new-folder.parent}"
+}
+```
+
+## Argument Reference
+
+The following arguments are supported:
+
+* `display_name` - (Required) The folder's display name.
+
+* `parent` - (Required) The resource name of the parent Folder or Organization.
+
+## Attributes Reference
+
+In addition to the arguments listed above, the following attributes are exported:
+
+* `name` - The resource name of the Folder. This uniquely identifies the folder.