Suggested Edits for Network chapter

Hey @arturo! I really enjoyed this chapter. You tackle some pretty big ideas (ones that obviously aren't even specific to oF) in a manageably abstract way. I made changes directly to the `chapter.md` file as well as added **[BD: some notes]**. A few more suggestions as well:

- Perhaps it would be helpful to add a sentence or two describing what a packet actually is. You refer to it multiple times throughout the chapter (and it is a very important concept) but I didn't see it described (at least from a high level explanation).
- It might be helpful to briefly describe what an IP address is in case someone has managed to make it that far in the book without knowing (which is unlikely).
- Pick a "you", "we", "our" style and stick with it. You alternate often between "we" and "you". I changed a few when they occurred in the same sentence, but didn't want to take the liberty to choose one for you.