Make it clearer what name you should use in your Git settings (also on GitHub)

[AnnikaLau]

Users should always use their full name in the Git config, on GitHub and on GitLab, so it is clear that the commits come from the same person. This was not clear to many participants.

[mjaehn]

@AnnikaLau
Should be clear now in https://github.com/C2SM/git-course/blob/review_beginner/beginner/Exercise_1_basic_commands.md