[AIRFLOW-720] Add Shopkick to Airflow users

Closes apache#1962 from ecesena/patch-1

README.md

@@ -131,6 +131,7 @@ Currently **officially** using Airflow:
 1. [Qubole](https://qubole.com) [[@msumit](https://github.com/msumit)]
 1. [Scaleway](https://scaleway.com) [[@kdeldycke](https://github.com/kdeldycke)]
 1. [Sense360](https://github.com/Sense360) [[@kamilmroczek](https://github.com/KamilMroczek)]
+1. [Shopkick](https://shopkick.com/) [[@shopkick](https://github.com/shopkick)]
 1. [Sidecar](https://hello.getsidecar.com/) [[@getsidecar](https://github.com/getsidecar)]
 1. [SimilarWeb](https://www.similarweb.com/) [[@similarweb](https://github.com/similarweb)]
 1. [SmartNews](https://www.smartnews.com/) [[@takus](https://github.com/takus)]