Update loading.js (#8035)

show how options can be set

Author: quide

Diff for: js/angular/service/loading.js

@@ -19,7 +19,8 @@ var LOADING_TPL =
  * .controller('LoadingCtrl', function($scope, $ionicLoading) {
  *   $scope.show = function() {
  *     $ionicLoading.show({
- *       template: 'Loading...'
+ *       template: 'Loading...',
+ *       duration: 3000
  *     }).then(function(){
  *        console.log("The loading indicator is now displayed");
  *     });