It really isn't that hard to do.
Just click on the image button in the markdown bar, or Ctrl+G, paste the image URL in the pop-up box and it should appear.
Remember to use the image URL. Right-click on the image, and click 'Copy Image URL' to get it. (In Chrome anyway, if it's different in other browsers, tell me) The URL you used in the example does not link directly to a image, it links to a webpage, so it won't show up as an image.
Hope I helped. :)