Update README.md
Add Golang Rotterdam Meetup
@@ -3325,6 +3325,7 @@ _Where to discover new Go libraries._
- [Golang Paris](https://www.meetup.com/Golang-Paris/)
- [Golang Poland](https://www.meetup.com/Golang-Poland/)
- [Golang Pune](https://www.meetup.com/Golang-Pune/)
+- [Golang Rotterdam](https://www.meetup.com/golang-rotterdam/)
- [Golang Singapore](https://www.meetup.com/golangsg/)
- [Golang Stockholm](https://www.meetup.com/Go-Stockholm/)
- [Golang Sydney, AU](https://www.meetup.com/golang-syd/)
