Add polished to index page

[merlinoa]

Once we get the polished intro video finished we will replace the "Shiny Apps" section with the polished intro video, a short explanation of polished, and a link to polished.tech.

We can move the explanation of what Shiny apps are to the "Shiny" page and put it in a top banner.

I will make these changes to the website once y'all finish up the intro video.

[merlinoa]

done