Merge EbookFoundation#7033 into normalize-authoring-format

Solve conflicts with branch 'upstream/main' until this PR/commit adding theirs resources too behind conflictive hunk

Author: davorpa

books/free-programming-books-langs.md

@@ -2005,6 +2005,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 ### QML
 
 * [Qt5 Cadaques](http://qmlbook.github.io) - Juergen Bocklage-Ryannel, Johan Thelin (HTML, PDF, ePub) (:construction: *in process*)
+* [Qt6 Book](https://www.qt.io/product/qt6/qml-book/preface-preface) - Johan Thelin, Jürgen Bocklage-Ryannel, Cyril Lorquet (HTML, PDF) (:construction: *in process*)
 
 
 ### R