Including doc for personal newbie error case.

docs/content/error/$injector/unpr.ngdoc

@@ -69,3 +69,16 @@ angular.module('myModule', [])
 ```
 
 Use the `$controller` service if you want to instantiate controllers yourself.
+
+Attempting to inject a scope object anything that´s not a controller or a directive,
+for example a service, will also throw an `Unknown provider` error:
+or mistakenly registering your controller as a service( believe me, it happens) an expecting
+a scope injection.
+
+```
+angular.module('myModule', [])
+  .service('MyController', ['$scope', function($scope) {
+    // This controller throws an unknown provider error because
+    // a scope object cannot be injected into a service.
+  }]);
+```