docs: add Superstardle in the wild (#1768)

README.md

@@ -216,6 +216,7 @@ reusable visualization charts or library without having to learn d3. No more sel
 - WHO Coronavirus (COVID-19) Dashboard is built on top of `vx`, earlier version of `visx`. ([Demo](https://covid19.who.int/))
 - [Fig Stats](https://fig-stats.com) - Figma community plugin & widget analytics
 - [Physician.FYI](https://physician.fyi) - Explore physicians' disciplinary history
+- [Index by Superstardle](https://index.superstardle.com), [Salaries by Superstardle](https://salaries.superstardle.com) - Explore sports teams and superstars in the world of underdogs and salaries
 
 Have a project that's using `visx`? Open a pull request and we'll add it to the list.