README: Update ActionController::Resources reference

Closes [#436][]

Remove reference to the now defunct `ActionController::Resources`.
Replace with a reference and link to
[ActionDispatch::Routing::Mapper::Resources][].

[#436]: #436
[ActionDispatch::Routing::Mapper::Resources]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html

Co-authored-by: Tomislav Simnett <tom@initforthe.com>

Author: seanpdoyle

README.md

@@ -3,7 +3,7 @@
 Active Resource (ARes) connects business objects and Representational State Transfer (REST)
 web services. It implements object-relational mapping for REST web services to provide transparent
 proxying capabilities between a client (Active Resource) and a RESTful service (which is provided by
-Simply RESTful routing in `ActionController::Resources`).
+RESTful routing in [ActionDispatch::Routing::Mapper::Resources](https://edgeapi.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html)).
 
 ## Philosophy