First draft of the introduction

Rewrote the introduction as a usecase.

Pulled the introduction into a separate file.

This is a first draft but thought I'd get out a general idea of the introduction I had out as soon as possible.
We decided to leave out casual search in the introduction entirely since it would be defined in the problem description. Which also explains why we limit ourselves to that.

But this was something that ended up being discusses in today's meeting.