Update bootcamp FAQ about "Checking out others' PRs"

[ezio-melotti]

I wanted to pull a PR branch and I was looking up "Checking out others' PRs", and the options were either to install gh, hub, or creating a Git alias.

Since I wanted a less permanent solution, I created this PR to show the commands individually before suggesting adding them as an alias. In addition I replaced checkout with the more modern switch, and capitalized "Git".

Another possible solution is to add the contributor's repo as a remote and fetch their branch from there, but I didn't want to add yet another solution. If people want to add it, we can create another PR.

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📚 Documentation preview 📚: https://cpython-devguide--1694.org.readthedocs.build/