fix: Update SchemaAwareStreamWriter comment to down recommend it. (#2195)

* fix: update the comment in SchemaAwareStreamWriter about when the feature is actually disabled

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Author: yirutang

google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/SchemaAwareStreamWriter.java

@@ -43,6 +43,13 @@
  * StreamWriter functions, but also provides an additional feature: schema update support, where if
  * the BigQuery table schema is updated, users will be able to ingest data on the new schema after
  * some time (in order of minutes).
+ *
+ * <p>NOTE: The schema update ability will be disabled when you pass in a table schema explicitly
+ * through the writer. It is recommended that user either use JsonStreamWriter (which fully manages
+ * table schema) or StreamWriter (which accepts proto format in raw and user will handle the schema
+ * update event themsevles). If you use this class, you need to be very cautious about possible
+ * mistmach between the writer's schema and the input data, any mismatch of the two will cause data
+ * corruption.
  */
 public class SchemaAwareStreamWriter<T> implements AutoCloseable {
   private static final Logger LOG = Logger.getLogger(SchemaAwareStreamWriter.class.getName());