Lesson 6 and 7 updates

[CalRobert]

I just worked through lesson 6 and 7 and thought I'd note a few things that were helpful to me.

• I was doing these lessons on a different computer (and day) than lesson 1, so a reminder of the data loaded from lesson 1 might help
• Fixed some simple typos
• Noted that if you try to save a PDF to a directory that doesn't exist, it will fail.