Add a doc reference on header's region for highlighting purposes

[chiefGui]

I know that you already had placed a "Docs" reference on "Quick Links" section, but I think it need to be more highlighted.

My suggest goes to a link after "Marionette.js on GitHub" called "Read the documentation". It's an important thing that people – mainly beginners – lost themselves until get right to the point.

Also, I think it's an easy approach to implement and you haven't put too much effort on it to turn it real.

Finally, this suggestion was born when I tried to find out where you placed the official Docs – I had to scroll in and out some times to get onto the documentation.

[jamesplease]

Thanks @chiefGui – we're working on a complete redesign of the www, though, so the change will be much bigger than this!

There will be a nav bar with the docs on the new design.

Closing as a dupe of #77 and #70