Add page for CS9

docs/distributions/cs9.md

+# CentOS Stream 9
+
+## Practical info
+
+!!! danger ""
+    Upstream support : End of RHEL9 “full support” phase (Estimated 2027)
+
+CentOS Stream 9's updates work the same way as [CS8](cs8.md), check that page
+for the full details. Some key differences are:
+
+  * The [Nomad job](https://gitlab.cern.ch/linuxsupport/cronjobs/stream9_snapshots/)
+  * Creates snapshots in `/mnt/data1/dist/cern/centos/s9-snapshots/`
+  * Maintains the symlinks from `s9` and `s9-testing`, etc.
+  * Freeze file is `.freeze.s9all`
+  * Forced update file is `.forcemove.s9`

mkdocs.yml

@@ -25,6 +25,7 @@ nav:
     - 'Distributions':
         - 'CC7': distributions/cc7.md
         - 'CS8': distributions/cs8.md
+        - 'CS9': distributions/cs9.md
         - 'Docker images': distributions/docker.md
         - 'OpenStack': distributions/openstack.md
         - 'Architecture': distributions/architecture.md