Doc: Updated the image URL

The existing HTTP url for logo.png was automatically
redirected to an HTTPS url which fails without SSL. So
updated the example to use different HTTP url.

Also updated another image URL, which is invalid now.

Task-number: QTBUG-35557
Change-Id: I793fc5ebda64b21f443da7db9ecda76ae951d5bf
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>