Document steps specific for Qt and its tools and needed to publish apps on App Store

There is a steady demand on the user side to get a guide about steps needed to build, package and sign a Qt-based app so that can be deployed on Apple App Store, for example, https://forum.qt.io/topic/138341/mac-deployment-issues.

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When using Xcode for development with Apple-only frameworks, this process is fully integrated in the Xcode IDE and the user does not need to deal with most details. Using Qt requires several manual steps on the console. This might be too advanced for many Qt users since many Qt users come to Qt on macOS and iOS from other plarforms and do not have a long-term experience with publishing to App Store(s)

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FYI: Another guide for a similar issue but with Python: https://github.com/nyavramov/python_app_mac_app_store

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