Issue title: Totally unable to get started; consider posting quickstart example?
 Issue body: Hey there,

I've been really excited to try FakeS3 ever since I heard about it. I love the idea of being able to develop code against S3 even when I'm offline.

I finally got around to it, but unfortunately I'm having a _ton_ of trouble figuring out how to use it for even something as basic as accessing an image from my web browser. I'm a Ruby noob unfortunately, so I'm also not having any luck trying to debug.

I'm on Mac OS X 10.7.5 (Lion), running the system default Ruby 1.8.7. I installed fakes3 via `sudo gem install fakes3` (just `gem install fakes3` gave me a permissions error), which installed FakeS3 0.1.5.

I tried starting it with `-p 4567 -r ~/Dropbox`, to see if I could browse my Dropbox files via FakeS3. Going to http://localhost:4567/ indeed showed the top-level directories in my Dropbox, but trying to browse to any sub-directory, or any individual file within any of those sub-directories, e.g. http://localhost:4567/Pictures/Misc/pixel.gif, always resulted in a 404.

I saw that indeed, FakeS3 was thinking each of those top-level dirs were buckets, and you've documented that it's recommended to use hostname-style requests, so I added `s3.amazonaws.com` and `dropbox.s3.amazonaws.com` to my `/etc/hosts` and ran with `-r ~/`, and indeed, I'm now able to view my home directory top-level dirs as buckets at http://s3.amazonaws.com:4567/. Unfortunately, I see the same buckets at http://dropbox.s3.amazonaws.com:4567/. And still, I can't access any file, e.g. http://dropbox.s3.amazonaws.com:4567/Pictures/Misc/pixel.gif or http://s3.amazonaws.com:4567/Dropbox/Pictures/Misc/pixel.gif.

I've done a bunch more experimenting, and still can't manage to just view a simple image in my browser. What am I doing wrong?

My sincere apologies if I'm missing something obvious, and thanks for your help. It might be helpful to have a simple "quickstart" example in the readme. If you'd like, I'd be happy to submit one after I figure this out.

Thanks!

 Comments: 
 Comment 0: Re-inquiring about this. Would love to use!

 Comment 1: @aseemk Not sure if fakes3 is the best solution to browse your pictures in the browser. I'm using it for local development and to be able to run my tests offline. For that it works perfect. 

 Comment 2: @aseemk, I agree with @reiz. Unfortunately, you can't point S3 at an arbitrary directory and have it serve the directory as if it were served from S3.  You have to give it a dedicated directory and fill that directory by doing S3 put calls.  

If you want to serve files from a current directory over http, I have found this one liner works well:
python -m SimpleHTTPServer

 Comment 3: No worries guys, this explains it perfectly:

> Unfortunately, you can't point S3 at an arbitrary directory and have it serve the directory as if it were served from S3. You have to give it a dedicated directory and fill that directory by doing S3 put calls.

I was under the mistaken impression that FakeS3 worked purely via the file system. Thanks for clarifying!

It'd still be great if I could get experience the functionality in _some_ way without writing a bunch of code first, but I understand that might be difficult or impractical.

 Comment 4: (By "some way", I mean e.g. like the AWS S3 console lets me get a sense of S3.)

 Comment 5:     Unfortunately, you can't point S3 at an arbitrary directory and have it serve the directory as if it were served from S3. You have to give it a dedicated directory and fill that directory by doing S3 put calls.

Jesus, that ought to be at the top of the README. This project has been a colossal waste of time for me.
 Comment 6: @SeanHayes [S3Proxy](https://github.com/andrewgaul/s3proxy) can serve existing directories and files, although only newly created objects will have all content metadata, e.g., ETag.
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