modules/git-workshop.md: Udacity courses aren't directly available anymore #36
Description
https://classroom.udacity.com/courses/ud123/lessons/1b369991-f1ca-4d6a-ba8f-e8318d76322f/concepts/63a6f935-dea7-43c2-aaa3-61deea5070c8 and https://classroom.udacity.com/courses/ud123/lessons/1b369991-f1ca-4d6a-ba8f-e8318d76322f/concepts/8a5af628-7a18-49cf-bbc8-02691762f862 (see https://github.com/kottans/git-course/blob/master/modules/git-workshop.md#:~:text=Mac/Linux%20Setup%2C%20Windows%20Setup. )are not directly available anymore.
Suggested fix: replace links' targets with similar resources.