docs(forms): ngSubmit is an output property of NgForm directive (#3056)

incorporates and closes PR #3040

public/docs/ts/latest/guide/forms.jade

@@ -575,8 +575,8 @@ figure.image-display
   trigger a form submit because of its type (`type="submit"`).
 
   A "form submit" is useless at the moment.
-  To make it useful, we'll update the `<form>` tag with another Angular directive, `NgSubmit`,
-  and bind it to the `HeroFormComponent.submit()` method with an  event binding
+  To make it useful, bind the `NgForm` directive's `ngSubmit` event property (in the `<form>` tag) 
+  to the `HeroFormComponent.submit()` method:
 +makeExample('forms/ts/app/hero-form.component.html', 'ngSubmit')(format=".")
 
 :marked
@@ -671,7 +671,7 @@ figure.image-display
 
   - An Angular HTML form template.
   - A form component class with a `Component` decorator.
-  - The `ngSubmit` directive for handling the form submission.
+  - Handling form submission by binding to the `NgForm.ngSubmit` event property.
   - Template reference variables such as `#heroForm`, `#name` and `#power`.
   - The `[(ngModel)]` syntax and a `name` attribute for two-way data binding, validation and change tracking.
   - The reference variable’s `valid` property on input controls to check if a control is valid and show/hide error messages.