Document GitHub CLI

[ezio-melotti]

https://cli.github.com/ should be documented in https://devguide.python.org/gitbootcamp/, on its own FAQ and/or integrated with the other FAQs.

Useful commands (shared on Discord):

• gh auth login (once)
• gh pr create: to create a PR
• gh pr checkout: to checkout others' PRs
• gh config set git_protocol ssh (once): to be able to push to others' PRs
• gh config set browser "/Applications/Firefox.app/Contents/MacOS/firefox": to set the browser

[erlend-aasland]

Note, there is already a short mention of GitHub CLI: https://devguide.python.org/gitbootcamp/#downloading-other-s-patches