Add dataloader in golang. (#123)

Author: appleboy

README.md

@@ -468,6 +468,8 @@ Looking to get started with a specific back-end? Try the [loaders in the example
   * [bs-dataloader](https://github.com/ulrikstrid/bs-dataloader)
 * Java
   * [java-dataloader](https://github.com/graphql-java/java-dataloader)
+* Golang
+  * [Dataloader](https://github.com/nicksrandall/dataloader)
 
 ## Video Source Code Walkthrough