Clarified a statement which suggested $scope was injectable into factories.

Per the docs at https://docs.angularjs.org/error/$injector/unpr

Attempting to inject a scope object into anything that's not a controller or a directive, for example a service, will also throw an Unknown provider: $scopeProvider <- $scope error.

Author: jedgell

README.md

@@ -329,7 +329,7 @@ While this guide explains the *what*, *why* and *how*, I find it helpful to see
 
   *Why?*: `controllerAs` is syntactic sugar over `$scope`. You can still bind to the View and still access `$scope` methods.
 
-  *Why?*: Helps avoid the temptation of using `$scope` methods inside a controller when it may otherwise be better to avoid them or move them to a factory. Consider using `$scope` in a factory, or if in a controller just when needed. For example when publishing and subscribing events using [`$emit`](https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$emit), [`$broadcast`](https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$broadcast), or [`$on`](https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$on) consider moving these uses to a factory and invoke from the controller.
+  *Why?*: Helps avoid the temptation of using `$scope` methods inside a controller when it may otherwise be better to avoid them or move the method to a factory, and reference them from the controller. Consider using `$scope` in a controller only when needed. For example when publishing and subscribing events using [`$emit`](https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$emit), [`$broadcast`](https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$broadcast), or [`$on`](https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$on) consider moving these uses to a factory and invoke from the controller.
 
   ```javascript
   /* avoid */