docs(input): provide explanation of how ngModel will affect the local scope

Author: mrlucmorin

src/ng/directive/input.js

@@ -1087,7 +1087,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
  * @element input
  *
  * @description
- * Is directive that tells Angular to do two-way data binding. It works together with `input`,
+ * Is a directive that tells Angular to do two-way data binding. It works together with `input`,
  * `select`, `textarea`. You can easily write your own directives to use `ngModel` as well.
  *
  * `ngModel` is responsible for:
@@ -1098,6 +1098,10 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
  * - keeping state of the control (valid/invalid, dirty/pristine, validation errors),
  * - setting related css class onto the element (`ng-valid`, `ng-invalid`, `ng-dirty`, `ng-pristine`),
  * - register the control with parent {@link ng.directive:form form}.
+ * 
+ * Note: `ngModel` will try to bind to the property given by evaluating the expression on the
+ * current scope. If the property doesn't already exist on this scope, it will be created
+ * implicitly and added to the scope.
  *
  * For basic examples, how to use `ngModel`, see:
  *