Note about importing from 'firebase'

Author: jamesdaniels

docs/Auth-with-Ionic2.md

@@ -263,6 +263,7 @@ Update the service with the following code.
 import { Observable } from 'rxjs/Observable';
 import { Injectable } from '@angular/core';
 import { AngularFireAuth } from 'angularfire2/auth';
+// Do not import from 'firebase' as you'll lose the tree shaking benefits
 import * as firebase from 'firebase/app';
 
 @Injectable()
@@ -469,6 +470,7 @@ your ```auth-service.ts``` code should look like this.
 import { Observable } from 'rxjs/Observable';
 import { Injectable } from '@angular/core';
 import { AngularFireAuth } from 'angularfire2/auth';
+// Do not import from 'firebase' as you'll lose the tree shaking benefits
 import * as firebase from 'firebase/app';
 
 import { Platform } from 'ionic-angular';