[AIRFLOW-XXX] Add Grab to the list of Airflow users (apache#5485)

[ci skip]

README.md

@@ -217,6 +217,7 @@ Currently **officially** using Airflow:
 1. [Global Fashion Group](http://global-fashion-group.com) [[@GFG](https://github.com/GFG)]
 1. [GoDataDriven](https://godatadriven.com/) [[@BasPH](https://github.com/basph), [@danielvdende](https://github.com/danielvdende), [@ffinfo](https://github.com/ffinfo), [@Fokko](https://github.com/Fokko), [@gglanzani](https://github.com/gglanzani), [@hgrif](https://github.com/hgrif), [@jrderuiter](https://github.com/jrderuiter), [@NielsZeilemaker](https://github.com/NielsZeilemaker)]
 1. [GovTech GDS](https://gds-gov.tech) [[@chrissng](https://github.com/chrissng) & [@datagovsg](https://github.com/datagovsg)]
+1. [Grab](https://www.grab.com/sg/) [[@calvintran](https://github.com/canhtran)]
 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)]