I don't remember since when AngularJS does not allow this anymore.
What you need to do is to include the AngularJS Sanitize library. You can download the sanitize library somewhere here: https://code.angularjs.org/1.2.16/
In your module
angular.module('myModule', ['ngSanitize'])
In your template
<div ng-bind-html="stage.description"></div>