QDesktopServices porting notes: fix copy/paste error and add link.

Change-Id: I593d0527b0db4785b5645f6fb9d599bfbaceec64
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>