Update gb-readme.md with links to Dutch translation (#878)

Author: bobkosse

gb-readme.md

@@ -29,6 +29,7 @@ Translations:
 - [Français](https://goosegeesejeez.gitbook.io/apprendre-go-par-les-tests)
 - [한국어](https://miryang.gitbook.io/learn-go-with-tests/)
 - [Türkçe](https://halilkocaoz.gitbook.io/go-programlama-dilini-ogren/)
+- [Nederlands](https://bobkosse.gitbook.io/leer-go-met-tests)
 
 ## Background