[AIRFLOW-614][AIRFLOW-1] Add Madrone as Airflow user

Closes apache#1866 from mbreining/master

README.md

@@ -116,6 +116,7 @@ Currently **officially** using Airflow:
 1. [LingoChamp](http://www.liulishuo.com/) [[@haitaoyao](https://github.com/haitaoyao)]
 1. [Lucid](http://luc.id) [[@jbrownlucid](https://github.com/jbrownlucid) & [@kkourtchikov](https://github.com/kkourtchikov)]
 1. [Lyft](https://www.lyft.com/)[[@SaurabhBajaj](https://github.com/SaurabhBajaj)]
+1. [Madrone](http://madroneco.com/) [[@mbreining](https://github.com/mbreining) & [@scotthb](https://github.com/scotthb)]
 1. [Markovian](https://markovian.com/) [[@al-xv](https://github.com/al-xv), [@skogsbaeck](https://github.com/skogsbaeck), [@waltherg](https://github.com/waltherg)]
 1. [MFG Labs](https://github.com/MfgLabs)
 1. [Nerdwallet](https://www.nerdwallet.com)