Add more visual diagrams

[mattb5]

What is really helping me now in this lesson is when Jeff drew this feature /unit router diagram on the board. I'm a STRONG visual learner and this really helped me envision the logic and hierarchy of appropriate tests.

Perhaps you want to place that diagram in the README as well?

Thanks :) -Matt

[payne-chris-r]

@jrhorn424 do you remember what Matty-Buff is talking about? Can you replicate tomorrow?

[jrhorn424]

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