URL modified

I've modified the URL of image location in the tutorial that was not working.

code:  cmd =  "Example: img = Image('http://www.simplecv.org/sites/all/themes/simplecv/images/logo.png')"

Now the image is loaded perfectly.

![simplecv](https://f.cloud.github.com/assets/2399519/153661/34d8727c-75ff-11e2-8a38-67eb50b97b93.png)