fix a desription error in sysctl file. (#7666)

modified:   docs/concepts/cluster-administration/sysctl-cluster.md

docs/concepts/cluster-administration/sysctl-cluster.md

@@ -130,19 +130,21 @@ to schedule those pods onto the right nodes.
 
 ## PodSecurityPolicy Annotations
 
-The use of sysctl in pods can be controlled via annotations on the PodSecurityPolicy.
+The use of sysctl in pods can be controlled via annotation on the PodSecurityPolicy.
 
-Here is an example, it authorizes binding user creating pod with corresponding
-_safe_ and _unsafe_ sysctls.
+Sysctl annotation represents a whitelist of allowed safe and unsafe sysctls
+in a pod spec. It's a comma-separated list of plain sysctl names or sysctl patterns
+(which end in `*`). The string `*` matches all sysctls.
+
+Here is an example, it authorizes binding user creating pod with corresponding sysctls.
 
 ```yaml
 apiVersion: extensions/v1beta1
 kind: PodSecurityPolicy
 metadata:
   name: sysctl-psp
   annotations:
-    security.alpha.kubernetes.io/sysctls: 'kernel.shm_rmid_forced'
-    security.alpha.kubernetes.io/unsafe-sysctls: 'net.ipv4.route.*,kernel.msg*'
+    security.alpha.kubernetes.io/sysctls: 'net.ipv4.route.*,kernel.msg*'
 spec:
  ...
 ```