fix missing entries in user guide's table of contents

[ianspektor]

Using python comments inside a markdown cell messes with the table of contents, since it (buggily) interprets it as an H1 heading (which makes all the headers after this one hidden, since mkdocs expects a single H1 at the top of the file).

Solution is to either not use those comments (and pass that text to above/below the code cell if possible, or to use same-line comments, i.e. instead of this:

# This is a comment that messes up the ToC
<code>

do this

<code>  # This is a comment that doesn't mess up the ToC

note that this only applies to ``` code blocks inside markdown cells, comments inside code cells are fine.

[DonBraulio]

Ooh nice catch! I would've been ages to figure out this one 😅