Clarify JSON array ingestion behavior for S3 log files

aws/logs_monitoring/README.md

@@ -282,6 +282,17 @@ If you still couldn't figure out, please create a ticket for [Datadog Support][1
 
 If your logs contain an attribute that Datadog parses as a timestamp, you need to make sure that the timestamp is both current and in the correct format. See [Log Date Remapper][24] to learn about which attributes are parsed as timestamps and how to make sure that the timestamp is valid.
 
+### S3 log files containing JSON arrays are ingested as a single event
+
+The Forwarder ingests each line of a log file as a separate event. If your S3 log file contains a JSON array (for example, `[{...}, {...}]`), the entire array is treated as a single log event. Datadog pipelines and processors cannot split a JSON array into multiple individual events after ingestion.
+
+To ensure each log entry is ingested as a separate event, format your log files as newline-delimited JSON (NDJSON), where each JSON object is on its own line:
+
+```json
+{"key": "value1"}
+{"key": "value2"}
+```
+
 ### Issue creating S3 triggers
 
 In case you encounter the following error when creating S3 triggers, we recommend considering following a fanout architecture proposed by AWS [in this article](https://aws.amazon.com/blogs/compute/fanout-s3-event-notifications-to-multiple-endpoints/)