POST request with data/parameters using Request class

[Steven Bara]

The documentation says:

You can create a request and then send the request with the client when you're ready:

use GuzzleHttp\Psr7\Request;

$request = new Request('PUT', 'http://httpbin.org/put');
$response = $client->send($request, ['timeout' => 2]);

But how do I create a POST request with parameters/data to send?