Merge pull request phpredis#2011 from feverxai/patch-1

Update sentinel.markdown

Author: michael-grunder

sentinel.markdown

@@ -16,6 +16,7 @@ Redis Sentinel also provides other collateral tasks such as monitoring, notifica
 *persistent*: String, persistent connection id (optional, default is NULL meaning not persistent)  
 *retry_interval*: Int, value in milliseconds (optional, default is 0)  
 *read_timeout*: Float, value in seconds (optional, default is 0 meaning unlimited)  
+*auth*:String, or an Array with one or two elements, used to authenticate with the redis-sentinel. (optional, default is NULL meaning NOAUTH)
 
 ##### *Example*
 
@@ -25,6 +26,7 @@ $sentinel = new RedisSentinel('127.0.0.1', 26379, 2.5); // 2.5 sec timeout.
 $sentinel = new RedisSentinel('127.0.0.1', 26379, 0, 'sentinel'); // persistent connection with id 'sentinel'
 $sentinel = new RedisSentinel('127.0.0.1', 26379, 0, ''); // also persistent connection with id ''
 $sentinel = new RedisSentinel('127.0.0.1', 26379, 1, null, 100); // 1 sec timeout, 100ms delay between reconnection attempts.
+$sentinel = new RedisSentinel('127.0.0.1', 26379, 0, NULL, 0, 0, "secret"); // connect sentinel with password authentication
 ~~~
 
 ### Usage