Mention the need to reboot.

Author: jovial

releasenotes/notes/bump-ubuntu-snapshots-2023-09-15-22ca5250d40bd5b6.yaml

@@ -4,4 +4,5 @@ security:
     Bumps Ubuntu repository snapshots and container images to bring in latest
     security patches. This includes the microcode to patch Inception
     (CVE-2023-20569) and Downfall (CVE-2022-40982). Zenbleed (CVE-2023-20593)
-    was patched in the previous snapshot bump.
+    was patched in the previous snapshot bump. To apply the microcode updates,
+    it is recommended to reboot each host after upgrading all of the packages.