Fix readme

Author: MarkusG

readme.md

@@ -45,8 +45,8 @@ You only need four lines of code, to generate and view your first QR code.
 ```csharp
 QRCodeGenerator qrGenerator = new QRCodeGenerator();
 QRCodeData qrCodeData = qrGenerator.CreateQrCode("The text which should be encoded.", QRCodeGenerator.ECCLevel.Q);
-QRCode qrCode = new QRCode(qrCodeData);
-Bitmap qrCodeImage = qrCode.GetGraphic(20);
+QRCode qrCode = new PngByteQRCode(qrCodeData);
+byte[] qrCodeImage = qrCode.GetGraphic(20);
 ```
 
 ### Optional parameters and overloads