Add preload_scope example to README

README.md

@@ -49,6 +49,27 @@ Call `preload` when defining your field:
   end
  end
 
+### `preload_scope`
+Starting with Rails 4.1, you can scope your preloaded records by passing a valid scope to [`ActiveRecord::Associations::Preloader`](https://apidock.com/rails/v4.1.8/ActiveRecord/Associations/Preloader/preload). Scoping can improve performance by reducing the number of models to be instantiated and can help with certain business goals (e.g., only returning records that have not been soft deleted).
+
+This functionality is surfaced through the `preload_scope` option:
+
+ PostType = GraphQL::ObjectType.define do
+  name 'Post'
+
+  field :comments, !types[!CommentType] do
+  preload :comments
+  preload_scope ->(args, ctx) { Comment.where(deleted_at: nil) }
+
+  # Resolves with records returned from the following query:
+  # SELECT "comments".*
+  # FROM "comments"
+  # WHERE "comments"."deleted_at" IS NULL
+  # AND "comments"."post_id" IN (1, 2, 3)
+  resolve ->(obj, args, ctx) { obj.comments }
+  end
+ end
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.