Update firestore-bigquery-export/functions/src/index.ts

Co-Authored-By: Jan Wyszynski <wyszynski@google.com>

Author: fredzqm

firestore-bigquery-export/functions/src/index.ts

@@ -34,7 +34,7 @@ exports.fsexportbigquery = functions.handler.firestore.document.onWrite(
     try {
       const changeType = getChangeType(change);
       await eventTracker.record([{
-        timestamp: context.timestamp,
+        timestamp: context.timestamp, // This is a Cloud Firestore commit timestamp with microsecond precision.
         operation: changeType,
         documentName: context.resource.name,
         eventId: context.eventId,