refine NextMarker comments (#8450)

cmd/object-api-datatypes.go

@@ -220,12 +220,12 @@ type ListObjectsInfo struct {
 	// by max keys.
 	IsTruncated bool
 
-	// When response is truncated (the IsTruncated element value in the response
-	// is true), you can use the key name in this field as marker in the subsequent
+	// When response is truncated (the IsTruncated element value in the response is true),
+	// you can use the key name in this field as marker in the subsequent
 	// request to get next set of objects.
 	//
-	// NOTE: This element is returned only if you have delimiter request parameter
-	// specified.
+	// NOTE: AWS S3 returns NextMarker only if you have delimiter request parameter specified,
+	//       MinIO always returns NextMarker.
 	NextMarker string
 
 	// List of objects info for this request.