[AIRFLOW-724] Adding City of San Diego to Airflow users

Closes apache#1965 from MrMaksimize/sandiego_use

README.md

@@ -97,6 +97,7 @@ Currently **officially** using Airflow:
 1. [Clairvoyant](https://clairvoyantsoft.com) [@shekharv](https://github.com/shekharv)
 1. [Clover Health](https://www.cloverhealth.com) [[@gwax](https://github.com/gwax) & [@vansivallab](https://github.com/vansivallab)]
 1. Chartboost [[@cgelman](https://github.com/cgelman) & [@dclubb](https://github.com/dclubb)]
+1. [City of San Diego](http://sandiego.gov) [[@MrMaksimize](https://github.com/mrmaksimize), [@andrell81](https://github.com/andrell81) & [@arnaudvedy](https://github.com/arnaudvedy)]
 1. [Cotap](https://github.com/cotap/) [[@maraca](https://github.com/maraca) & [@richardchew](https://github.com/richardchew)]
 1. [Digital First Media](https://www.digitalfirstmedia.com/) [[@duffn](https://github.com/duffn)]
 1. [Easy Taxi](http://www.easytaxi.com/) [[@caique-lima](https://github.com/caique-lima) & [@WesleyBatista](https://github.com/WesleyBatista)]