Add initial qmltc tool documentation with introduction,
compilation process picture, description and limitations
To simplify the description, we can consider some simple
application. The same app can additionally become a test
scenario for qmltc and a showcase of its capabilities
Task-number: QTBUG-84368
Pick-to: 6.3
Change-Id: If6d586a8c68f48d17133b25170d0fff627e2066c
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Andrei Golubev