Almost works in dev container

[jschirrmacher]

Still, there is an error message when I call ./generateHTML.sh:

FAILURE: Build failed with an exception.

* What went wrong:
Task 'generateHTML' not found in root project 'aoc-2020'.

[rdmueller]

thanx for this PR. I have opened up a new repository for this year: https://github.com/docToolchain/aoc-2021 / https://aoc-2021.netlify.app/

I will check your changes to see which problem they address.