Add explanations (a README.md)

[Naereen]

Hi,
It's a great project, thanks for putting it up here!
But I'm sure every visitor could benefit from a little more details!

• Where does the source code come from ?
• Is there any reference explaining/detailing/proving that this is truly the original source code for morris-worm?
• Any details regarding how to compile, run and test it?

Thanks in advance!

(I found out about this project from this article)