Add instructions for adding ssh keys to Github

[nouredd2]

Some students don't have their keys already set up, so they get stuck on cloning their repos. It would be worth it to add instructions for generating keys and adding them to Github.

• One thing to be aware of, is that a bunch of them confuse gitbash with the WSL terminal, so they generate keys on gitbash and then clone from the WSL terminal, which will not be using the same keys.