docs(GCS+gRPC): add contact info

google/cloud/storage/doc/storage-grpc.dox

@@ -5,8 +5,14 @@
 The GCS C++ client library includes an optional plugin to access GCS via gRPC.
 When using GCS from Google Compute Engine (GCE) this plugin can enable higher
 total throughput across large workloads that run on hundreds or thousands of
-VMs.  Note that this feature is not GA. Consult with your account manager to be
-included in the early access program.
+VMs.
+
+@warning At present, GCS gRPC is GA with Allowlist. To access this API,
+  kindly contact the Google Cloud Storage gRPC team at
+  gcs-grpc-contact@google.com with a list of GCS buckets you would like to
+  Allowlist. Please note that while the **service** is GA (with Allowlist),
+  the client library features remain experimental and subject to change
+  without notice.
 
 ## Release Notes
 
@@ -35,6 +41,10 @@ differently from the REST-based implementation.
    of calling these functions. Our telemetry shows these functions are not used
    via the C++ client library, but you should keep this in mind before deciding
    to use these functions in new code.
+1. The functions to create, list, query, and delete HMAC keys and notifications
+   are unavailable in gRPC. Our telemetry indicates that these functions are
+   never used in C++, and therefore we do not anticipate this can cause
+   problems.
 
 [OCC loop]: https://en.wikipedia.org/wiki/Optimistic_concurrency_control
 [file a bug]: https://github.com/googleapis/google-cloud-cpp/issues/new/choose

google/cloud/storage/grpc_plugin.h

@@ -25,9 +25,7 @@ namespace cloud {
  * Contains experimental features for the GCS C++ Client Library.
  *
  * @warning The types, functions, aliases, and objects in this namespace are
- *   subject to change without notice. Some of these features depend on aspects
- *   of the service that are not generally available, do not have an SLA, and
- *   may require projects to be allow-listed.
+ *   subject to change without notice.
  */
 namespace storage_experimental {
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
@@ -41,9 +39,12 @@ GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
  *   and `InsertObject()` use gRPC.
  * - "metadata": use gRPC for all operations.
  *
- * @warning GCS+gRPC is an experimental feature of the C++ client library, and
- *   subject to change without notice.  The service itself is not generally
- *   available, does not have an SLA and requires projects to be allow-listed.
+ * @warning At present, GCS gRPC is GA with Allowlist. To access this API,
+ *   kindly contact the Google Cloud Storage gRPC team at
+ *   gcs-grpc-contact@google.com with a list of GCS buckets you would like to
+ *   Allowlist. Please note that while the **service** is GA (with Allowlist),
+ *   the client library features remain experimental and subject to change
+ *   without notice.
  */
 struct GrpcPluginOption {
   using Type = std::string;
@@ -52,13 +53,14 @@ struct GrpcPluginOption {
 /**
  * Create a `google::cloud::storage::Client` object configured to use gRPC.
  *
- * @note The Credentials parameter in the configuration is ignored. The gRPC
- *     client only supports Google Default Credentials.
- *
  * @param opts the configuration parameters for the Client.
  *
- * @warning This is an experimental feature, and subject to change without
- *     notice.
+ * @warning At present, GCS gRPC is GA with Allowlist. To access this API,
+ *   kindly contact the Google Cloud Storage gRPC team at
+ *   gcs-grpc-contact@google.com with a list of GCS buckets you would like to
+ *   Allowlist. Please note that while the **service** is GA (with Allowlist),
+ *   the client library features remain experimental and subject to change
+ *   without notice.
  *
  * @par Example
  * @snippet storage_grpc_samples.cc grpc-read-write