Create package declaration to run dataloaden

ref: vektah/dataloaden#35

docs/content/reference/dataloaders.md

@@ -83,6 +83,7 @@ doesnt have generics. Instead we generate the code manually for our instance.
 go get github.com/vektah/dataloaden
 mkdir dataloader
 cd dataloader
+echo 'package dataloader' > gen.go
 go run github.com/vektah/dataloaden UserLoader int *gqlgen-tutorials/dataloader/graph/model.User
 ```