Python 3.8: Add walrus operator discussion

[rsokl]

Probably should live in control flow

[samaocarpenter]

I'll get on this - will try to finish this up this weekend

[rsokl]

@HardBoiled800 Let's hold off on this for now. You have a few balls in the air right now and this may be a tricky sections to cover in the right amount of detail.

We can loop back once your other WIPs are finished

[samaocarpenter]

@rsokl Sorry, I got a bit overenthusiastic there! I'll focus on my current stuff for now!