Update home page with screenshots of the app.

[zorn]

As a follow-up to #100 I think I'd like to add screenshots and some better spacing/visuals to the home page.

Will delay this work until other pages are updated since I want up-to-date screenshots.

Other notes here:

https://mastodon.social/@boredzo/113630063088774317

I'd say the main thing would be to leaven the section with the three steps. Add empty space, bump up the font size (maybe only for each one's main verb-phrase), and add simple line-art illustrations of each step.

Also, “Use Cases” should be reframed as more “What is ranked voting good for?” Keep the examples, but also explain how ranked voting creates better decisions (because ranked voting selections tend to be acceptable to a larger majority of voters, rather than favorites of a few).