doc: update README
doc: update README

- Note what's in the screenshot.
- Delete "Design" section.
- Add some detail to other sections.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent