Add a reminder about what the question mark does

[maneesha]

No description provided.

[maxim-belkin]

Thank you for so many contributions, Maneesha! Please see my comments below.

[maneesha]

Catching up on a very old issue!
I am fine with any of the options listed. I originally put in this PR because the ? notation is used in the example, and so the explanation should refer to what is in the example.

[tobyhodges]

I'm helping the current lesson Maintainers process outstanding pull requests on this repository, in preparation for transition to the new lesson infrastructure. Thank you for contributing, @maneesha.

I agree that the lesson could be improved with an explanation of ?, given that it is used in the example code block. Of the three options @maxim-belkin listed, I would be most in favour of the second ("Expand the sentence to mention the built-in help() function + clarify that in Jupyter notebooks we can use topic? notation"), so I am going to suggest a change to the PR.

We have until the end of this month to get these changes merged, before the Workbench transition forces us to close the PR.