Clarify secrets file mode might be read in decimal notation

Fixes: kubernetes/kubernetes#33475

Author: rata

docs/user-guide/secrets/index.md

@@ -344,6 +344,9 @@ In this case, the file resulting in `/etc/foo/my-group/my-username` will have
 permission value of `0777`. Owing to JSON limitations, you must specify the mode
 in decimal notation.
 
+Note that this permission value might be displayed in decimal notation if you
+read it later.
+
 **Consuming Secret Values from Volumes**
 
 Inside the container that mounts a secret volume, the secret keys appear as