Clarify sentinel constructor parameters

Fix: #1188

Author: byroot

README.md

@@ -103,7 +103,7 @@ To connect using Sentinel, use:
 SENTINELS = [{ host: "127.0.0.1", port: 26380 },
              { host: "127.0.0.1", port: 26381 }]
 
-redis = Redis.new(url: "redis://mymaster", sentinels: SENTINELS, role: :master)
+redis = Redis.new(name: "mymaster", sentinels: SENTINELS, role: :master)
 ```
 
 * The master name identifies a group of Redis instances composed of a master
@@ -129,6 +129,12 @@ SENTINELS = [{ host: '127.0.0.1', port: 26380, password: 'mysecret' },
 redis = Redis.new(name: 'mymaster', sentinels: SENTINELS, role: :master)
 ```
 
+Also the name can be passed as an url:
+
+```ruby
+redis = Redis.new(name: "redis://mymaster", sentinels: SENTINELS, role: :master)
+```
+
 ## Cluster support
 
 [Clustering](https://redis.io/topics/cluster-spec). is supported via the [`redis-clustering` gem](cluster/).