Make shell example cut-and-pastable

[bjnath]

Users will want to cut and paste the example at the left onto the shell, so it should be presented as one block, with the intervening text (e.g., "Create a 2-D array") being changed into comments.

Playing the role of dumb user I cut and pasted just the middle section since it seemed the most interesting, and of course saw

[rgommers]

That's a fair comment. I liked the look of proper text rather than code comments, but copy-pasting is useful. I can take this along in the final cleanup before launch.