Polish the example a little bit

[fakedrake]

This is related to issue #21 , a main branch commit fixes the fundamental problem, I just added some easy to infer stuff and some info in the README.

[stylewarning]

Overall I'm happy with the direction of this PR, and I'm grateful for the contribution. However, I'm hesitant to merge this in its current state.

1. I think things need to be stated in terms of the most vanilla possible setup with Quicklisp.
2. Changing the Makefile to use SBCL_SRC=$(HOME)/.roswell/src/sbcl-2.2.2 isn't a good idea to stipulate here I don't think.
3. One shouldn't modify system-index manually, and instead it should be deleted and automatically regenerated.
4. I think changes to the example code itself should be a separate commit from changes to documentation.

I think @kartik-s can help split this out and add some documentation to help make things clearer with your provided feedback.

[karlosz]

Closing, since pull request #29 addresses the same issue and has been merged.