feature(limit-count): supported global limit count with redis server.

doc/plugins/limit-count-cn.md

@@ -49,6 +49,37 @@ curl -i http://127.0.0.1:9080/apisix/admin/routes/1 -X PUT -d '
 然后在 route 页面中添加 limit-count 插件：
 ![](../images/plugin/limit-count-2.png)
 
+如果你需要一个集群级别的流量控制，我们可以借助 redis server 来完成。不同的 APISIX 节点之间将共享流量限速结果，实现集群流量限速。
+
+请看下面例子：
+
+```shell
+curl -i http://127.0.0.1:9080/apisix/admin/routes/1 -X PUT -d '
+{
+    "uri": "/index.html",
+    "plugins": {
+        "limit-count": {
+            "count": 2,
+            "time_window": 60,
+            "rejected_code": 503,
+            "key": "remote_addr",
+            "policy": "redis",
+            "redis": {
+                "host": "127.0.0.1",
+                "port": 6379,
+                "timeout": 1001
+            }
+        }
+    },
+    "upstream": {
+        "type": "roundrobin",
+        "nodes": {
+            "39.97.63.215:80": 1
+        }
+    }
+}'
+```
+
 #### 测试插件
 上述配置限制了 60 秒内只能访问 2 次，前两次访问都会正常访问：
 ```shell

doc/plugins/limit-count.md

@@ -18,6 +18,7 @@
 ### example
 
 #### enable plugin
+
 Here's an example, enable the `limit count` plugin on the specified route:
 
 ```shell
@@ -47,6 +48,37 @@ You can open dashboard with a browser: `http://127.0.0.1:9080/apisix/dashboard/`
 Then add limit-count plugin:
 ![](../images/plugin/limit-count-2.png)
 
+If you need a cluster-level precision traffic limit, then we can do it with the redis server. The rate limit of the traffic will be shared between different APISIX nodes to limit the rate of cluster traffic.
+
+Here is the example:
+
+```shell
+curl -i http://127.0.0.1:9080/apisix/admin/routes/1 -X PUT -d '
+{
+    "uri": "/index.html",
+    "plugins": {
+        "limit-count": {
+            "count": 2,
+            "time_window": 60,
+            "rejected_code": 503,
+            "key": "remote_addr",
+            "policy": "redis",
+            "redis": {
+                "host": "127.0.0.1",
+                "port": 6379,
+                "timeout": 1001
+            }
+        }
+    },
+    "upstream": {
+        "type": "roundrobin",
+        "nodes": {
+            "39.97.63.215:80": 1
+        }
+    }
+}'
+```
+
 #### test plugin
 The above configuration limits access to only 2 times in 60 seconds. The first two visits will be normally:
 ```shell