Documentation/progressbar, suggestion of adding comment or CCS for demo

[trinitrotoluene76]

Hi, thanks for your amazing work, it's very helpfull for developper like me. I notice that the example of progress bar (http://filedropjs.org/#progress) isn't "plug & play": if you tried to modify basic.html with the example you didn't view the progressbar "bar_zone10". I suggest to add a little bit of ccs or a comment in the documentation span { display:block; background-color:red; width:0; height: 2px; }