[AIRFLOW-XXX] Added ThoughtWorks as user of Airflow in README (apache#4012)

Author: sann3

README.md

@@ -264,6 +264,7 @@ Currently **officially** using Airflow:
 1. [THE ICONIC](https://www.theiconic.com.au/) [[@revathijay](https://github.com/revathijay)] [[@ilikedata](https://github.com/ilikedata)]
 1. [Thinking Machines](https://thinkingmachin.es) [[@marksteve](https://github.com/marksteve)]
 1. [Thinknear](https://www.thinknear.com/) [[@d3cay1](https://github.com/d3cay1), [@ccson](https://github.com/ccson), & [@ababian](https://github.com/ababian)]
+1. [ThoughtWorks](https://www.thoughtworks.com/) [[@sann3](https://github.com/sann3)]
 1. [Thumbtack](https://www.thumbtack.com/) [[@natekupp](https://github.com/natekupp)]
 1. [Tictail](https://tictail.com/)
 1. [Tile](https://tile.com/) [[@ranjanmanish](https://github.com/ranjanmanish)]