[Development] Qt 6 co-installability with Qt 5

[Sune Vuorela]

On 2020-11-17, Kai Köhne <Kai.Koehne at qt.io> wrote:
> Why should the packages in the online installer change? They are hardly ever installed into some general directory.

To have documentation be "Run this command `foo`". not "If you are
running linux or mac and have gotten your Qt the normal way thru your
packagemanager, run `foo-qt6`, if you are on windows or have done the qt
installer, run `foo`"

/Sune