sockets with predis

If you use predis, the way to create the socket connection is

```php
$redis = new Predis_Client(array(
    'scheme' => 'unix',
    'path'   => $redis_server
  ));
```
I also included a switch for this: `$sockets`.

Also, there was a typo, `$reddis_server` instead of `$redis_server`.

Explained everything in `README.md`.