Add documentation for ingesting JSON to a ManagedStream

bigquery/storage/managedwriter/doc.go

@@ -262,5 +262,21 @@ https://pkg.go.dev/google.golang.org/api/option#WithGRPCConnectionPool
 
 A reasonable upper bound for the connection pool size is the number of concurrent writers for explicit stream
 plus the configured size of the multiplex pool.
+
+# Writing JSON Data
+
+As an example, you can refer to this integration test that demonstrates writing JSON data to a stream:
+https://github.com/googleapis/google-cloud-go/blob/7a46b5428f239871993d66be2c7c667121f60a6f/bigquery/storage/managedwriter/integration_test.go#L397
+
+This integration test assumes the destination table already exists. In addition, it relies upon having a definition of
+a BigQuery schema that is compatible with this table (for this example the schema is defined here:
+https://github.com/googleapis/google-cloud-go/blob/2020edff24e3ffe127248cf9a90c67593c303e18/bigquery/storage/managedwriter/testdata/schemas.go#L31).
+Given the schema, this test first utilizes the function setupDynamicDescriptors() to derive both a MessageDescriptor
+and DescriptorProto from the schema. This function is defined here:
+https://github.com/googleapis/google-cloud-go/blob/7a46b5428f239871993d66be2c7c667121f60a6f/bigquery/storage/managedwriter/integration_test.go#L100
+The test initializes the ManagedStream it will write to with the derived DescriptorProto. The test then iterates
+through each of the JSON rows to be written. For each row, it first dynamically creates an empty Message based on
+the derived MessageDescriptor. Then it loads the JSON row into the Message. Finally it generates protocol buffer
+bytes from the Message. These bytes are then sent to the ManagedStream within an AppendRows request.
 */
 package managedwriter