Add better explanation of Wercker setup
The current Linux setup has the installation output set to "-o /usr/local/bin/wercker". Apparently it is essential -- that is to say wercker will NOT run correctly -- unless this is also the location of the 'docker' executable file. The assumption -- which I ran across by accident -- is well stated in the response by hatchan to issue #255 where he says "...We require that the host that is running the docker daemon has the source directory on the same location as where wercker is running.
With Linux this isn't an issue since both are are the same."
Actually, there is no guarantee in Linux that the executables for any given package are in '/usr/local/bin'. This is a convenient convention, and certainly not unreasonable, but (in my system for example) 'docker' is located in '/usr/bin' which is also perfectly acceptable. For example, grub, node, npm and many other packages installed through apt end up there. I would strongly recommend that you add some notes in the documentation on this issue. There is no place that I could find that even suggests that this is a critical dependency.