[Git] Split into two different lectures

[hyendler]

Split the currently Git lecture into two different folders in the teaching-materials repo (you will need to fork and clone the repo to do this):

1. Git (slides 1 - 50 of current git lecture)
2. Github (slides 51 through 75)

This is linked to the large epic issue 485

[kate-stoner]

working on it with Sara

[stale]

This issue has been automatically marked as stale because it has not been updated in the last 30 days. It will be closed if no further activity occurs within the next 7 days. Feel free to reach out on the #opensource channel in our Slack team or mention an admin for further help and resources if they are needed.

[stale]

This issue has been automatically closed due to max staleness.
Thank you so much for your contributions to Girl Develop It SF.
Please feel free to open up another PR at any time. 💛

[stale]

This issue has been automatically marked as stale because it has not been updated in the last 30 days.
It will be closed if no further activity occurs within the next 7 days.
If needed, feel free to reach out on the #open-source channel in our Slack team.
You can also mention an admin for further help and resources. 😊

[stale]

This issue has been automatically closed due to max staleness.
Thank you so much for your contributions to Girl Develop It SF.
Please feel free to open up another PR at any time. 💛