update Readme

scripts/cleanup_clusters/README.md

@@ -6,6 +6,8 @@ Domain Admin user.  Before running this script, log in as that user: `gcloud aut
 
 Usage (from the main directory):
 
-```./cleanup_clusters/cleanup_clusters.sh [list|delete]```
+```./cleanup_clusters/cleanup_clusters.sh [list|delete] log_suffix```
 
 `list` will print out the list of old clusters but not delete them.  `delete` will actually delete them.
+
+`log_suffix` is a string (example: QA) to include in the log file name to distinguish it from other runs on the same day.