Updated lecture 2, added (extremely rough) graphs

Working on typing up my lecture 4 (Thursday, 11 September) notes - I will push these too as soon as I get them done.

I have a conflict on Tuesdays so I wouldn't mind sharing some of the note duties with someone who's planning on making the Tuesday lectures.

The graphs are super rough as I threw them together in graphviz real quick. I'll push some updates to them later