demonstrating mkdir upon introduction

[karenword]

I'm a member of The Carpentries Core Team and I'm submitting this issue on behalf of another member of the community. In most cases, I won't be able to follow up or provide more details other than what I'm providing below.

https://librarycarpentry.org/lc-shell/03-working-with-files-and-folders.html

Here we teach the mkdir command for the first time. I think it would be good for the learner if we just show the content of the shell-lesson folder (with ls), then teach mkdir, and then use ls to show that the new file (firstdir) was created. That way the learners can visually see what the command accomplished.