Reorganize the documentation

Will close issue #257 and #273 
Hmm, even I don't really know what this is saying :). What will I need to install? I think we should remove this entirely or be more clear about what we're talking about. It seems to me that the only things that I will need to worry about are Gaufrette/Flysystem, which we can talk about later. If 'm using Propel or Doctrine, I think this will clearly already be installed.