[AIRFLOW-XXX] Add Grab to companies list (apache#4041)

Author: chandulal

README.md

@@ -169,6 +169,7 @@ Currently **officially** using Airflow:
 1. [Glassdoor](https://github.com/Glassdoor) [[@syvineckruyk](https://github.com/syvineckruyk)]
 1. [Global Fashion Group](http://global-fashion-group.com) [[@GFG](https://github.com/GFG)]
 1. [GovTech GDS](https://gds-gov.tech) [[@chrissng](https://github.com/chrissng) & [@datagovsg](https://github.com/datagovsg)]
+1. [Grab](https://www.grab.com/sg/) [[@grab](https://github.com/grab)]
 1. [Gradeup](https://gradeup.co) [[@gradeup](https://github.com/gradeup)]
 1. [Grand Rounds](https://www.grandrounds.com/) [[@richddr](https://github.com/richddr), [@timz1290](https://github.com/timz1290), [@wenever](https://github.com/@wenever), & [@runongirlrunon](https://github.com/runongirlrunon)]
 1. [Groupalia](http://es.groupalia.com) [[@jesusfcr](https://github.com/jesusfcr)]