Add note about broken Secure boot

docs/project/scos-migration-faq.md

@@ -4,6 +4,7 @@
 
 This FAQ document relates to the builds of OKD that use CentOS Stream CoreOS (SCOS) after work done to stop using RHEL as the base for cluster components, as well as the upgrade path from pre-4.16 OKD FCOS/SCOS installations.
 
-*Holding Page*
+## Secure Boot
+Secure Boot is currently not supported on CentOS Stream CoreOS (SCOS). This is tracked in [RHEL-4391](https://issues.redhat.com/browse/RHEL-4391) and [rhboot/shim-review#399](https://github.com/rhboot/shim-review/issues/399).
 
 Please see the GitHub discussion at [this link](https://github.com/okd-project/okd/discussions/1922).