CMake docs should mention required module

Consider e.g. qt-add-tranlsations. https://doc.qt.io/Qt-6/qtlinguist-cmake-qt-add-translations.html . To use it, we need a

find_package(Qt6 Components REQUIRED <other stuff> LinguistTools)

However, that is neither evident from the linked page, nor from its direct parent page, https://doc.qt.io/Qt-6/qtlinguist-index.html

This is less problematic with the API in declarative, as there you most likely need find_package to link against the libraries. However, at least for tools and their corresponding commands, we should add some pointer to the documentation.