doc: modify ip restrictions plugin doc. (apache#1219)

doc/plugins/ip-restriction.md

@@ -87,11 +87,58 @@ HTTP/1.1 403 Forbidden
 {"message":"Your IP address is not allowed"}
 ```
 
+## Change the restriction
+
+When you want to change the whitelisted ip, it is very simple,
+you can send the corresponding json configuration in the plugin configuration,
+no need to restart the service, it will take effect immediately:
+
+```shell
+curl http://127.0.0.1:9080/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
+{
+    "uri": "/index.html",
+    "upstream": {
+        "type": "roundrobin",
+        "nodes": {
+            "127.0.0.1:1980": 1
+        }
+    },
+    "plugins": {
+        "ip-restriction": {
+            "whitelist": [
+                "127.0.0.2",
+                "113.74.26.106/24"
+            ]
+        }
+    }
+}'
+```
+
+## Test Plugin after restriction change
+
+Requests to `127.0.0.2`:
+
+```shell
+$ curl http://127.0.0.2:9080/index.html
+HTTP/1.1 200 OK
+...
+```
+
+Requests to `127.0.0.1`:
+
+```shell
+$ curl http://127.0.0.1:9080/index.html -i
+HTTP/1.1 403 Forbidden
+...
+{"message":"Your IP address is not allowed"}
+```
+
+
 ## Disable Plugin
 
 When you want to disable the `ip-restriction` plugin, it is very simple,
- you can delete the corresponding json configuration in the plugin configuration,
-  no need to restart the service, it will take effect immediately:
+you can delete the corresponding json configuration in the plugin configuration,
+no need to restart the service, it will take effect immediately:
 
 ```shell
 $ curl http://127.0.0.1:2379/v2/keys/apisix/routes/1 -X PUT -d value='