Updates to setup/README

[tshaffe1]

Going through the README, I had a few comments.

• The project directory layout is a little confusing. The README mentions going to hashfs/caching, but it's not immediately clear where that is. The repo itself is called hashfs and has a caching directory, but there's also a hashfs directory with its own caching subdirectory. If you'd like to keep both hashfs/caching and hashfs/hashfs/caching, you should be sure the README is unambiguous.
• CacheServer.py should use Python's argparse rather than messing with argv. Same advice for any argument parsing elsewhere.
• The README should be organized with a first-time setup section with pip, virtualenv, etc. and a separate section for initializing the environment after that, in case a user wants to run servers in different terminals.
• There should be some explanation of starting servers locally vs. pointing to another machine.
• The contents of demo.sh should be merged directly into the README, with explanation as appropriate. Also, one of the paths in that script has changed.
• The FUSE part should be expanded. The installation instructions should go in the setup section at the beginning, and there should be an example of running and configuring the FUSE module (and stopping it with fusermount).

It would also be a good idea to think about writing some automated tests and benchmarks (with instructions for running them in the README of course).