Conditional lesson - flesh out conditional lesson check for file section

[lwasser]

The first conditional lesson has a section that is not yet fleshed out.

To follow our activities, we could have them work on a conditional that checks if a file exists before opening it.
We can use the data here if we want as an example. the goal is to move away from. using Earthpy and, instead, using the publication data throughout these lessons.

You can see in the screenshot below that the old example was some boulder data used in a class i taught. Now let's swap this out using the JSON data in this repo.