Guide: sessions is misleading regarding custom session adapters

[graywolf]

Here https://github.com/hanami/hanami.github.io/blob/build/source/guides/head/actions/sessions.md it says that

Custom storage technologies are autoloaded via require "rack/session/#{ adapter_name }". 

However, when I create file with class Rack::Session::Foo loadable by require 'rack/session/foo', it's not autoloaded and server complains about uninitialized constant. At the moment I just require it manualy at top of application.rb, but the guide should probably be reworded somehow (not sure how).