Update modal-controller.ts

I added documentation on how to use a modal container component in an Ionic app. This has had a lot of discussion in ionic-team#8151, and is minimally documented, so I took a stab at documenting it.

src/components/modal/modal-controller.ts

@@ -112,6 +112,25 @@ import { DeepLinker } from '../../navigation/deep-linker';
  *
  * }
  * ```
+ *
+ * A common issue is that a developer may try to implement navigation in a modal, but when you try NavController.push(),
+ * you will notice that the status bar on iOS gets cut off. The proper way to implement navigation in a modal is to 
+ * make the modal component a navigation container, and set the root page to the page you want to show in your modal.
+ *
+ * ```ts
+ * @Component({
+ *   template: '<ion-nav [root]="rootPage" [rootParams]="rootParams"></ion-nav>'
+ * })
+ * export class MyModalWrapper {
+ *   rootPage = 'MyModalContentPage'; // This is the page you want your modal to display
+ *   rootParams;
+ * 
+ *   constructor(navParams: NavParams, private viewCtrl: ViewController) {
+ *       this.rootParams = Object.assign({}, navParams.data, {viewCtrl: viewCtrl});
+ *       // This line will send the view controller into your child views, so you can dismiss the modals from there.
+ *   }
+ * }
+ * ```
  * @demo /docs/demos/src/modal/
  * @see {@link /docs/components#modals Modal Component Docs}
  */