add some basic documentation for CustomQueries

app/services/hyrax/custom_queries.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+module Hyrax
+  ##
+  # These custom queries are used throughout the Hyrax codebase. They are
+  # intended for use with Valkyrie's custom query interface (i.e. you
+  # shouldn't call classes in this namespace directly except to configure that
+  # interface).
+  #
+  # In this namespace, we provide default/reference implementations, with the
+  # restriction that they cannot use any adapter-specific knowledge. I.e. these
+  # queries use the Valkyrie core queries and client side data manipulation
+  # only. This restriction limits performance expectations for these
+  # implementations, but guarantees a basic level of compatibility for all
+  # conforming Valkyrie adapters.
+  #
+  # In order for a Valkyrie adapter to be "supported" by Hyrax, these queries
+  # should be individually evaluated for performance when using the adapter.
+  # Where appropriate, optimized implementations should be provided taking
+  # advantage of backend-specific query features.
+  #
+  # @see https://github.com/samvera/valkyrie/wiki/Queries#custom-queries
+  # @see https://github.com/samvera/hyrax/wiki/Hyrax-Valkyrie-Usage-Guide#custom-queriesy
+  module CustomQueries
+  end
+end