docs: Add warning description of force sync options

Signed-off-by: kkk777-7 <kota.kimura0725@gmail.com>

docs/user-guide/sync-options.md

@@ -168,8 +168,12 @@ metadata:
 ## Force Sync
 
 For certain resources you might want to delete and recreate. e.g. job resources that should run every time when syncing.
-In such cases you might use `Force=true` sync option in target resources annotation:
 
+!!! warning
+      During the sync process, the resources will be synchronized using the 'kubectl delete/create' command.
+      This sync option has a destructive action, which could cause an outage for your application.
+
+In such cases you might use `Force=true` sync option in target resources annotation:
 ```yaml
 metadata:
   annotations: