add test script

aws/whats-new/README.md

@@ -1,5 +1,11 @@
 # What's New on our AWS
 
+## 2025-12-31: Test script for cross-account roles
+
+In order to validate the cross account roles work, we created a script to use it. This script can be replicated to perform per-account tasks within
+the organization.  We perhaps will make this into a python module so it becomes easier to plug in one's own script without copy/paste of the tool.
+See it at [test-cross-org.py](https://github.e.it.census.gov/terraform/support/tree/master/local-app/python-tools/test-cross-organization).
+
 ## 2025-12-30: New Stackset implementing cross-account roles
 
 A new stackset in all organizations (ent-gov, ent-ew, lab-gov) which implements two cross-account roles,