docs(ngmodule): improved NgModule summary description

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

@@ -7,7 +7,12 @@ block includes
 :marked
   **Angular Modules** help organize an application into cohesive blocks of functionality.
 
-  An Angular Module _class_ is adorned with the **NgModule** decorator that defines metadata about the module. 
+  An Angular Module is a _class_ adorned with the **@NgModule** decorator function.
+  `_@NgModule` takes a metadata object that tells Angular how to compile and run module code. 
+  It identifies the module's _own_ components, directives and pipes, 
+  making some of them public so external components can use them. 
+  It may add service providers to the application dependency injectors. 
+  And there are more options covered here. 
 
   This chapter explains how to **create** `NgModule` classes and how to load them, 
   either immediately when the application launches or later, as needed, via the [Router](router.html).  
@@ -74,10 +79,9 @@ a#angular-modularity
 
   An Angular module is a class decorated with `@NgModule` metadata. The metadata:
 
-  * declare which components, directives and pipes  _belong together_.
+  * declare which components, directives and pipes  _belong_ to the module.
   * make some of those classes public so that other component templates can use them.
-  * hide other classes as implementation details.
-  * import other modules with the components, directives and pipes it needs.
+  * import other modules with the components, directives and pipes needed by the components in _this_ module.
   * provide services at the application level that any application component can use.
 
   Every Angular app has at least one module class, the _root module_.