Readme: fix image URL and credit zodiacon

Document SkinManager.

#5: System wide Light mode does not allow changing the context menu c…

…olor

GitHub seems to be incapable of invalidating their cache on an old ve…

…rsion of images, so rename the files.

#3: WPF demo does not show a dark title bar, fails on CI but not locally

2.0.0 release

Added Readme.