Clarify the content of Safety-Critical UI with Qt Quick Designer page

https://doc.qt.io/QtSafeRenderer/qtsr-safety-features.html

--> this page contains Qt Quick Designer related content (that's ok!) and also some other content, like updating the .pro file and building a project. This other content should be documented in a separate page.

https://doc.qt.io/QtSafeRenderer/qtsr-workflow.html could provide a table of contents for all sub-pages related to the developing UI with QSR.