Make test.sh better

[jcbhmr]

problem: the test.sh is confusing
i.e. not everyone (me included) know what the heck happens in that magic bash script 🤣

this isn't a major problem, but it is a thing to do that i think is a good idea. 😉

solution 1: make it a python script instead with more friendly programming language syntax
solution 2: add a bunch of comments

i vote solution 1. i originally tried to do this in the #20 pr, but was too complicated at the time. time for another crack at it?

[eitsupi]

I think that the content of this script is confusing, not because of the language, but because there is no way to check the intermediate file (the generated devcontainer.json).

My preference is to use Makefiles to split tasks so they can be executed in order.