Re-order discrete plotting section

[zenalapp]

The discrete part has good content but I think it could be reordered a bit because it didn't flow super well. Maybe just has to be taught a few times to work out the kinks.

One idea:

• Explain that aes can go inside a function earlier on (when collapsing everything together after making the 1st plot).
• Move part with geom_point(aes(size=pop)) to exercise after talk about color/fill.

[zenalapp]

@MrFlick did you/will you have the opportunity to work on this? Just wondering if we should assign it to someone else.

[MrFlick]

@zenalapp I wasn't able to make any edits on this. I can't quite come up with a narrative that makes the transition as smooth as I would like. I think someone with a fresh set of eyes would be better.

[zenalapp]

Sounds good - thanks for all your help!