Add image demonstrating meaning of "mirror learner's environment"

[ndporter]

How could the content be improved?

Per discussion on #1043 it would be ideal to have a persistent (e.g. learners can review after the training) example of what it looks like to mirror or not the learner's environment.

Which part of the content does your suggestion apply to?

https://carpentries.github.io/instructor-training/instructor/17-live.html

[brownsarahm]

Image(s) of this could be hard because it is so many different tools we teach, plus screenshots require frequent updating.

Maybe we aim for a reminder of checking what the defaults are for each one.

Related, I have had dark/light mode questions lately and I have said that now that it is such a common device level choice, I think we can trust most people to be used to it and use what works best for the teaching context (eg in person some projectors/screens wash out at one extreme) and instructor (for online esp) but make note of that. I hedged that it was my personal thought, because we do not have official guidance that is more detailed other than attempting to minimize extraneous cognitive load.