Add tutorial documentation

I worked through this a while back, and the biggest stumbling blocks I had were literally figuring out how to run a test, and then figuring out what order these are supposed to be done in.

The rest of it was pretty straightforward, from looking at Mux2 and then working through things in order. There were a few things that were non-obvious, where I had to look up things in documentation. I jotted those down. With those added, I believe the problems can be solved without referring to outside docs, although the hints here are a bit terse.

A co-worker was interested in Chisel, and I was going to send him the notes I wrote down, but I might as well submit a pull request, in case this might help other folks.