Including in the Qt SCXML documentation the additional library that needs to be installed for it

Qt user was wondering why Scxml is not found and he could not find a named package in the Qt Online installers Additional Libraries.

Qt Scxml is included in the Qt State Machines:

https://doc.qt.io/qt-6/qtstatemachine-index.html

User had following suggestions:
"It would be useful to document in Scxml documentation that what module it belongs to"

https://doc.qt.io/qt-6/qtscxml-index.html