Deprecate omitting Redis server URI for createClient()

Author: clue

README.md

@@ -121,12 +121,6 @@ $factory->createClient('localhost:6379')->then(
 );
 ```
 
-You can omit the complete URI if you want to connect to the default address `localhost:6379`:
-
-```php
-$factory->createClient();
-```
-
 You can omit the port if you're connecting to the default port 6379:
 
 ```php
@@ -145,6 +139,15 @@ You can optionally include a path that will be used to select (SELECT command) t
 $factory->createClient('localhost/2');
 ```
 
+[Deprecated] You can omit the complete URI if you want to connect to the default
+address `localhost:6379`. This legacy API will be removed in a future
+`v2.0.0` version, so it's highly recommended to upgrade to the above API.
+
+```php
+// deprecated
+$factory->createClient();
+```
+
 ### Client
 
 The `Client` is responsible for exchanging messages with Redis

src/Factory.php

@@ -44,7 +44,9 @@ public function __construct(LoopInterface $loop, $connector = null, ProtocolFact
     /**
      * create redis client connected to address of given redis instance
      *
-     * @param string|null $target
+     * @param string|null $target Redis server URI to connect to. Not passing
+     *     this parameter is deprecated and only supported for BC reasons and
+     *     will be removed in future versions.
      * @return \React\Promise\PromiseInterface resolves with Client or rejects with \Exception
      */
     public function createClient($target = null)