Adding Apache Superset to "In the Wild" section (#3003)

Apache Superset has been using Emotion for quite a while now (original proposal [here](apache/superset#9123), and best practices captured [here](https://github.com/apache/superset/wiki/Emotion-Styling-Guidelines-and-Best-Practices). We'd be proud to have our link on the roster!

README.md

@@ -110,6 +110,7 @@ Look here 👉 _[emotion babel plugin feature table and documentation](https://g
 - [cyberhaven.com](https://cyberhaven.com)
 - [CommercialRealEstate.com.au](https://www.commercialrealestate.com.au)
 - [codecademy.com](https://www.codecademy.com)
+- [Apache Superset](https://superset.apache.org/)
 
 ## Sponsors