Added a series of use case guidelines from Writing Effective Use Cases by Alistair Cockburn, with permission his permission.

I'm quite glad that I read his book, use cases always seemed rather useless, the stick figures and ellipses giving little meaningful information.  Ever since the introduction of the UML there has been a craze for drawing in software engineering, as if drawing enough pictures would do our work for us. His book, however, demonstrates how to leverage the power of use cases, not from a picture, but from text.