Update bulk.md (#4761)

Fixes #4706

Signed-off-by: Heather Halter <[email protected]>

_api-reference/document-apis/bulk.md

@@ -14,7 +14,7 @@ Introduced 1.0
 The bulk operation lets you add, update, or delete multiple documents in a single request. Compared to individual OpenSearch indexing requests, the bulk operation has significant performance benefits. Whenever practical, we recommend batching indexing operations into bulk requests.
 
 
-Beginning in OpenSearch 2.9, when indexing documents using the bulk operation, the document `_id` must be 512 MB or less in size.
+Beginning in OpenSearch 2.9, when indexing documents using the bulk operation, the document `_id` must be 512 bytes or less in size.
 {: .note}
 
 ## Example