STP-3724: Add info about SAT transition into CSM

- Describe SAT product/documentation changes and timing
- Provide links to new SAT info in CSM docs

docs/README.md

@@ -1,5 +1,14 @@
 # HPE Cray EX System Admin Toolkit (SAT) Guide
 
+**IMPORTANT:** Starting in CSM 1.6.0, SAT is fully included in CSM. There is no longer a separate SAT
+product stream to install. SAT 2.6 releases, which accompanied CSM 1.5, are the last releases of
+SAT as a separate product.
+
+Similarly, the SAT documentation moved to be fully included within the CSM documentation. Starting in
+CSM 1.6.0, find information on SAT in the
+[System Admin Toolkit (SAT) section](https://cray-hpe.github.io/docs-csm/en-16/operations/system_admin_toolkit/)
+of the [Cray System Management Documentation](https://cray-hpe.github.io/docs-csm/en-16/).
+
 ## [About SAT](about_sat/README.md)
 
 - [View SAT Documentation](about_sat/view_sat_docs.md)