adds a devcontainer

[unglaublicherdude]

I put some time into installing not the exact version, removing them again until suff actually workded. My Idea was to just contribute a devcontainer so that the versions of the dependencies are already correctly installed there and nobody has to try out stuff on their own system where they might already have other npm or yarn versions installed.

[lmiller1990]

Cool, nice job getting this running using docker. I won't merge this since I want the source code in master to match the exact one used in the course, but happy to leave this PR open for others who might want to use it.