Clean up tutorial 10 notebook

[acwooding]

• [ ] Suggest doing git init from the terminal (in fact, all of the terminal commands from the terminal)
• [ ] Exercise 6: be explicit about needing to edit environment.yml instead of requirement.txt
• [ ] Exercise 6: make a note to do git add -p and git reset -p in the terminal (must do it there because they are interactive)
• [ ] Exercise 6: indicate that we do NOT want to check in the notebook
• [ ] Add something at the end about actually checking in a notebook (once we are done the exercises)
• [ ] GitHub exercise: Make a note that we do NOT want to initialize with a README/LICENSE file as we've already created those
• [ ] add_sklearn exercise: add instructions fro checking out a new branch, reminder to use make requirements