The walkthrough:
* Creates a .slint file
* Explains Live Preview
* Shows Properties Editor
* Explains where to get help
No code change, this is all just added configuration/markdown/images.
Remove the Welcome page we had earlier (which does change some code).
Co-authored-by: Olivier Goffart <olivier@woboq.com>
Co-authored-by: Simon Hausmann <hausmann@gmail.com>
