I see on this page Bluemix Track and Plan provides burndown charts. How do I get to those?
Within your DevOps Services project dashboard click on the arrow on the right in Track&Plan button (first enable Track&Plan in Project Settings) and select Project Dashboard. In the Project Dashboard click on the button "Add widget" on top right to find all the available widgets. There you will find the Burndown Charts and many more (use the search field to filter them).