Document how to make Qt applications use less battery on macOS

I noticed that my app was using significant energy according to the battery menu thingy on macOS. I figured out that this is due to "Requires High Perf GPU" showing "Yes" in activity monitor. I looked around a bit and found QTCREATORBUG-11296​​​​​​​, with patches that fix it for Creator by setting NSSupportsAutomaticGraphicsSwitching to true in its Info.plist file. For my Qbs project, I did it like this:

    Properties {
        condition: qbs.targetOS.contains("macos")
        bundle.infoPlist: ({
            "NSSupportsAutomaticGraphicsSwitching": "true"
        })
    }

Now it's not listed as using significant energy or requiring a high performance GPU. I can't notice any difference in FPS in my app from (very) brief testing.

This seems like a very important thing for developers to know about.

This page could be a good place for it:

https://doc.qt.io/qt-5/macos-issues.html

Could also be good to link to any eventual documentation for this on https://doc.qt.io/qt-5/qtquick-performance.html.