fix missing images in episode 2

[bturkus]

not sure exactly how do do this myself, but there are some funky links and missing images in the Jupyter notebook episode. also wondering more generally if some of this could be trimmed down.

[nkrabben]

This is a pretty straight pull from a Carpentries lesson. I'll take another pass at cutting down. The markdown stuff is probably too much as is the window arrangement.