docs: add cluster shutdown and restart

Signed-off-by: Frank Yang <poan.yang@suse.com>

docs/advanced/cluster-shutdown.md

@@ -0,0 +1,21 @@
+---
+sidebar_position: 7
+sidebar_label: Cluster Shutdown and Restart
+title: "Cluster Shutdown and Restart"
+---
+
+## Shutdown a Harvester cluster
+
+To gracefully shutdown a Harvester cluster, please run the following steps to keep the data safe.
+
+1. Shutdown all VMs.
+2. Take backups for all VMs.
+3. Download all VM Images. (Since Harvester hasn't automatically backup VM Images in the backup target, you have to keep VM Images by yourself.)
+4. Shutdown all agent nodes.
+5. Shutdown all management nodes.
+
+## Restart a Harvester cluster
+
+1. Restart all management nodes.
+2. Restart all agent nodes.
+3. Restart all VMs.