Tell people not to install this addon. (#75)

README.md

@@ -1,3 +1,7 @@
+### WARNING
+__You probably don't need to use this addon__. Most of the use cases you'd use this addon for are perfectly achievable without this addon. Read the following blog post for more info:
+[Ember Best Practices: What are controllers good for?](https://dockyard.com/blog/2017/06/16/ember-best-practices-what-are-controllers-good-for)
+
 # ember-route-action-helper ![Download count all time](https://img.shields.io/npm/dt/ember-route-action-helper.svg) [![CircleCI](https://circleci.com/gh/DockYard/ember-route-action-helper.svg?style=shield)](https://circleci.com/gh/DockYard/ember-route-action-helper) [![npm version](https://badge.fury.io/js/ember-route-action-helper.svg)](https://badge.fury.io/js/ember-route-action-helper)
 
 **[ember-router-action-helper is built and maintained by DockYard, contact us for expert Ember.js consulting](https://dockyard.com/ember-consulting)**.