Update README.md

Fixed listing type in example of Listing class

Signed-off-by: Jérémie Fréreault <jerefrereault@hotmail.com>

README.md

@@ -55,7 +55,7 @@ Using the Listing Class
 use Shopiro\Listing;
 
 // Create a listing
-$response = Listing::create('type', ['data']);
+$response = Listing::create('marketplace_low_volume', ['data']);
 
 // Retrieve multiple listings
 $allListings = Listing::getAll(10, 0);