docs(header): update header markup

src/components/navbar/navbar.ts

@@ -62,26 +62,32 @@ class ToolbarBackground {
 /**
  * @name Navbar
  * @description
- * Navbar is a global level toolbar that gets updated every time a page gets
- * loaded. You can pass the navbar an `ion-title`, any number of buttons, a segment, or a searchbar.
+ * Navbar acts as the navigational toolbar, which also comes with a back
+ * button. A navbar can contain a `ion-title`, any number of buttons,
+ * a segment, or a searchbar. Navbars must be placed within an
+ * `<ion-header>` in order for them to be placed above the content.
  *
  * @usage
  * ```html
- * <ion-navbar *navbar>
- *   <button menuToggle>
- *     <ion-icon name="menu"></ion-icon>
- *   </button>
+ * <ion-header>
  *
- *   <ion-title>
- *     Page Title
- *   </ion-title>
- *
- *   <ion-buttons end>
- *     <button (click)="openModal()">
- *       <ion-icon name="options"></ion-icon>
+ *   <ion-navbar>
+ *     <button menuToggle>
+ *       <ion-icon name="menu"></ion-icon>
  *     </button>
- *   </ion-buttons>
- * </ion-navbar>
+ *
+ *     <ion-title>
+ *       Page Title
+ *     </ion-title>
+ *
+ *     <ion-buttons end>
+ *       <button (click)="openModal()">
+ *         <ion-icon name="options"></ion-icon>
+ *       </button>
+ *     </ion-buttons>
+ *   </ion-navbar>
+ *
+ * </ion-header>
  * ```
  *
  * @demo /docs/v2/demos/navbar/
@@ -221,9 +227,6 @@ export class Navbar extends ToolbarBase {
 
 /**
  * @private
- * Used to find and register headers in a view, and this directive's
- * content will be moved up to the common navbar location, and created
- * using the same context as the view's content area.
 */
 @Directive({
   selector: 'template[navbar]'