Initial Dox changes

This MR:

• changes parts of the README to be more useful for whoever visits the repository
• adds a basic Mainpage.dox for whoever visits the API page
• add an examples/ folder containing the tutorial example

The documentation for FormTextDelegate is not generated because of the following error:

ERROR:root:Failed to parse /home/blumen/gitstuff/kirigami-addons/src/mobileform/FormTextDelegate.qml
ERROR:root:Lexer error line 55: Expected token of type 'element', got 'char' instead

    signal linkActivated(link: string)
-----------------------------^

For AboutPage, it seems like Doxyqml thinks there might be an extraneous } ? But that's definitely not the case.

ERROR:root:Failed to parse /home/blumen/gitstuff/kirigami-addons/src/mobileform/AboutPage.qml
ERROR:root:Lexer error line 382: Unexpected token: Token(type='block_end', value='}', idx=14462)

}
^

For DatePicker this is expected because it isn't documented yet.