Missing data: Qt6 compiling dependencies

[teward]

The README is all written for Qt5. Do you have the dependencies for Qt6 builds? I would like to make sure the dependencies are properly addressed in Debian for the XCA packaging, which is currently still using Qt5 in 2.6.0 builds, because not everywhere in backports has Qt 6 currently. Therefore I'd like to get things set up properly for either version in the Debian packaging.

While I could probably figure out the dependencies, as your README defines the dependencies it's necessary for it to be updated (and this'll make sure I set the deps right on my end!)