Doc: Fix broken external link to Apple Developer page

Change link target so that it points to a location that is less prone
to change in the future. The original document is gone, and the
Apple Developer site has undergone major restructuring in the years
since. By pointing the user to the main landing page, our link will
likely work also in the future, even if Apple decides to redesign their
Apple Developer site.

Task-number: QTBUG-60494
Change-Id: Icff92dcbbe202bc5e2e46ba44eabac610f9b1899
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

doc/src/platforms/osx.qdoc

@@ -1006,7 +1006,7 @@
     When you are done linking your application to Qt, either
     statically or as frameworks, the application is ready to be
     distributed. For more information, refer to the
-    \l {https://developer.apple.com/library/mac/#documentation/ToolsLanguages/Conceptual/OSXWorkflowGuide/Introduction/Introduction.html}{Tools Workflow Guide}.
+    \l {https://developer.apple.com/}{Apple Developer} website.
 
     Although the process of deploying an application do have some
     pitfalls, once you know the various issues you can easily create