docs: add client options endpoint to doc.go
@@ -22,6 +22,24 @@ of sub-packages.
All clients in sub-packages are configurable via client options. These options are
described here: https://godoc.org/google.golang.org/api/option.
+## Endpoint Override
+
+Endpoint configuration is used to specify the URL to which requests are
+sent. It is used for services that support or require regional endpoints, as well
+as for other use cases such as [testing against fake
+servers](https://github.com/googleapis/google-cloud-go/blob/main/testing.md#testing-grpc-services-using-fakes).
+
+For example, the Vertex AI service recommends that you configure the endpoint to the
+location with the features you want that is closest to your physical location or the
+location of your users. There is no global endpoint for Vertex AI. See
+[Vertex AI - Locations](https://cloud.google.com/vertex-ai/docs/general/locations)
+for more details. The following example demonstrates configuring a Vertex AI client
+with a regional endpoint:
+
+ ctx := context.Background()
+ endpoint := "us-central1-aiplatform.googleapis.com:443"
+ client, err := aiplatform.NewDatasetClient(ctx, option.WithEndpoint(endpoint))
+
# Authentication and Authorization
All the clients in sub-packages support authentication via Google Application Default
