Add to instructor notes: consider data/plots/examples in context of workshop setting

[cfmw]

Hi - I think it's worth adding a comment in the instructor notes (_extras/guide.md) for instructors to consider the context in which they will be teaching a workshop and whether the data/plots/examples could be alienating to any of the learners that might be present. For example, Challenge 5 in "Creating Publication-Quality Graphics with ggplot2" may not be a sensitive example when teaching a workshop in an African setting. I recognize that "data are data," but explicitly suggesting that instructors consider the context of their workshop might be helpful. This would also be an approach to providing some resolution to Issue #456 , where BarshisLab pointed out that the same lesson involves plots where genocides can be easily identified.

[matthieu-bruneaux]

Thank you very much for bringing this forward @cfmw! I think this is a very valid and important point.

We definitely want the lesson material and the workshops based on it to be as inclusive and welcoming as possible, and I agree that it is important to be aware of potentially triggering data/examples.

Would you like to submit a PR with some updated instructor notes about this?