Link not working for MIT 8.421 and Theoretical Minimum from Stanford (Youtube)

[retrogtx]

[kritoke]

Looks like they re-arranged the url naming conventions. It should be Video Lectures
. Might be worth linking to just the original course instead to avoid future issues like this: Atomic and Optical Physics I. Looks like the youtube playlist is just different url now.

[kritoke]

#21 I have created a pull request to try to fix the youtube playlist url and several MIT links that are broken, moved them to link to course instead of direct link to videos (since they appear to have changed multiple times over the years).