add docs for resolver generation

docs/content/config.md

@@ -22,6 +22,11 @@ model:
   filename: models/generated.go
   package: models
 
+# Optional, turns on resolver stub generation
+resolver:
+  filename: resolver.go # where to write them
+  type: Resolver  # whats the resolver root implementation type called?
+
 # Tell gqlgen about any existing models you want to reuse for
 # graphql. These normally come from the db or a remote api.
 models: