edits for clustering and regionalization chapters

[ljwolf]

Question 6, @darribas writes:

We could recast this question to make it more practical, along the lines @ljwolf does in other chapters. For example, on this one, it could be:

• Re-run the analysis in the chapter w/ a different set of weights.
• Compare the resulting clusters visually
• What are the key differences between the two W's?
• How do you think such differences affect the final result?

Question 7, @darribas writes

This one I think it's pretty hard for an introductory text.

Question 8, @darribas writes

I'm not sure I understand this one