Draft MCU getting started documentation

One Overview page for MCU as part of our documentation.

1.  Create MCU QDS project (link to studio-projects.html referring to the wizard)
2. Some explanation... link to https://doc.qt.io/QtForMCUs-2.3/qtul-qtquick-api-differences.html#qt-quick-ultralite-vs-qt-quick but some short summary in our documentation.
3. Explain that QDS uses the QtQuick runtime for running and previewing
4. Explain what else is required to build and deploy an application. You have to install the MCU framework, some 4-5 sentences that explain how to go from a QDS project to an actual working MCU application.