docs(bigquery/storage/managedwriter): clarify experimental status
Package managedwriter provides an EXPERIMENTAL thick client around the BigQuery storage API's BigQueryWriteClient.
More information about this new write client may also be found in the public documentation: https://cloud.google.com/bigquery/docs/write-api
-It is EXPERIMENTAL and subject to change or removal without notice. This library is in a pre-alpha
-state, and breaking changes are frequent.
+It is EXPERIMENTAL and subject to change or removal without notice. This is primarily to signal that this
+package may still make breaking changes to existing methods and functionality.
Currently, this client targets the BigQueryWriteClient present in the v1 endpoint, and is intended as a more
feature-rich successor to the classic BigQuery streaming interface, which is presented as the Inserter abstraction
