docs(database): Updated 4. Querying lists (angular#572)

Updated the Query list Section to bring in consistency across other pages. Removed ModuleId to avoid errors. updated Selector, Component name. Added a sample data set at the end from completion point of view.

Author: mukesh51

docs/4-querying-lists.md

@@ -52,6 +52,8 @@ re-run queries when the observable emits a new value.
 
 This is the magic of AngularFire2.
 
+An RxJS Subject is imported below. A Subject is like an Observable, but can multicast to many Observers. Subjects are like EventEmitters: they maintain a registry of many listeners. See, [What is a Subject](http://reactivex.io/rxjs/manual/overview.html#subject) for more information.
+
 ```ts
 const subject = new Subject(); // import {Subject} from 'rxjs/Subject';
 const queryObservable = af.database.list('/items', {
@@ -81,8 +83,7 @@ import { AngularFire, FirebaseListObservable, FirebaseObjectObservable } from 'a
 import { Subject } from 'rxjs/Subject';
 
 @Component({
-  moduleId: module.id,
-  selector: 'app',
+  selector: 'app-root',
   template: `
   <ul>
     <li *ngFor="let item of items | async">
@@ -97,7 +98,7 @@ import { Subject } from 'rxjs/Subject';
   </div>
   `,
 })
-export class RcTestAppComponent {
+export class AppComponent {
   items: FirebaseListObservable<any[]>;
   sizeSubject: Subject<any>;
 
@@ -116,4 +117,19 @@ export class RcTestAppComponent {
 }
 ```
 
-###[Next Step: User Authentication](5-user-authentication.md)
++**To run the above example as is, you need to have sample data in you firebase database with the following structure:"**
+ 
+ ```ts
+   -|items
+       -|item1
+           -|size: small
+           -|text: sample small text
+       -|item2
+           -|size: medium
+           -|text: sample medium text
+       -|item3
+           -|size: large
+           -|text: sample large text    
+ ```
+
+###[Next Step: User Authentication](5-user-authentication.md)