added Glassdoor to "who uses airflow"

README.md

@@ -86,6 +86,7 @@ Currently **officially** using Airflow:
 * [Cotap](https://github.com/cotap/) [[@maraca](https://github.com/maraca) & [@richardchew](https://github.com/richardchew)]
 * Easy Taxi [[@caique-lima](https://github.com/caique-lima)]
 * [FreshBooks](https://github.com/freshbooks) [[@DinoCow](https://github.com/DinoCow)]
+* [Glassdoor](https://github.com/Glassdoor) [[@syvineckruyk](https://github.com/syvineckruyk)]
 * [Handy](http://www.handy.com/careers/73115?gh_jid=73115&gh_src=o5qcxn) [[@marcintustin](https://github.com/marcintustin) / [@mtustin-handy](https://github.com/mtustin-handy)]
 * [Holimetrix](http://holimetrix.com/) [[@thibault-ketterer](https://github.com/thibault-ketterer)]
 * [Hootsuite](https://github.com/hootsuite)