Made a quick note about the object. tab completion feature in IPython and ? help function. I found this to be helpful in the classes in letting them know how they can fend for themselves more quickly with a feature that they might otherwise not find.

Modified callout to emphasise this is an IPython feature.

Added a note that: 1) help(data.cumprod) = data.cumprod?
and 2) that this displays the function's docstring.

fixed quote-mark error in last commit