doc(otel): GA (#12748)

Author: dbolduc

CHANGELOG.md

@@ -122,6 +122,12 @@ the APIs in these libraries are stable, and are ready for production use.
 
 New `*Client` for conversational search.
 
+### [OpenTelemetry](/google/cloud/opentelemetry/README.md)
+
+Features to instrument the Google Cloud C++ libraries for [distributed tracing]
+using [OpenTelemetry] are now GA. See the [quickstart][otel-quickstart] within
+the library to learn more about these tools.
+
 ### [Policy Troubleshooter](/google/cloud/policytroubleshooter/README.md)
 
 Remove `PoliciesClient`. This client was placed in the wrong library. The
@@ -4381,6 +4387,7 @@ releases. The relevant notes are:
 [cloud-iot-shutdown]: https://cloud.google.com/iot/docs/release-notes#August_16_2022
 [cloud-run-jobs]: https://cloud.google.com/run/docs/managing/job-executions
 [dataproc-node-groups]: https://cloud.google.com/dataproc/docs/guides/node-groups/dataproc-driver-node-groups
+[distributed tracing]: https://opentelemetry.io/docs/concepts/observability-primer/#distributed-traces
 [functions-v2]: https://cloud.google.com/functions/docs/concepts/version-comparison
 [github-cpp-common]: https://github.com/googleapis/google-cloud-cpp-common
 [google.pubsub.v1.schemaserviceclient]: https://cloud.google.com/pubsub/docs/reference/rpc/google.pubsub.v1#google.pubsub.v1.SchemaService
@@ -4395,7 +4402,9 @@ releases. The relevant notes are:
 [modern-table-ctor]: https://github.com/googleapis/google-cloud-cpp/blob/62740c8e9180056db77d4dd3e80a6fa7ae71295a/google/cloud/bigtable/table.h#L182-L214
 [monitoring-snooze]: https://cloud.google.com/monitoring/alerts/snooze
 [nlohmann-json-gh]: https://github.com/nlohmann/json.git
+[opentelemetry]: https://opentelemetry.io/
 [oss-cxx-support]: https://opensource.google/documentation/policies/cplusplus-support
+[otel-quickstart]: https://github.com/googleapis/google-cloud-cpp/blob/main/google/cloud/opentelemetry/quickstart
 [product-launch-stages]: https://cloud.google.com/products/#product-launch-stages
 [pub/sub lite]: /google/cloud/pubsublite/README.md
 [resource-manager-tags]: https://cloud.google.com/resource-manager/docs/tags/tags-overview

google/cloud/opentelemetry/README.md

@@ -10,9 +10,8 @@ The C++ client libraries are already instrumented to collect traces. You can
 enable the collection and export of traces with minimal changes to your
 application. It is not necessary to instrument your application too.
 
-:construction:
-
-This library is **experimental**. Its APIs are subject to change without notice.
+While this library is **GA**, please note that the Google Cloud C++ client
+libraries do **not** follow [Semantic Versioning](https://semver.org/).
 
 ## Quickstart