Adding Text to Static Analysis Chapter

I've added the beginning (intro sections) of the chapter. I'm going to add 4 more sections, one for each of three "checks" that TypeCheck can make.

There probably needs to be more "this is how this works in Julia" notes added to the early code examples.
This is a super great example of the types of instrumentation and experimentation that engineers often need to do to understand what their problem actually is.