[github] Authenticate with GitHub using a token

First, you need to create a personal access token (PAT). This is described here: https://help.github.com/articles/creating-an-access-token-for-command-line-use/

Laughably, the article tells you how to create it, but gives absolutely no clue what to do with it. After about an hour of trawling documentation and Stack Overflow, I finally found the answer:

$ git clone https://github.com/user-or-organisation/myrepo.git
Username: <my-username>
Password: <my-personal-access-token>

I was actually forced to enable two-factor authentication by company policy while I was working remotely and still had local changes, so in fact it was not clone I needed, but push. I read in lots of places that I needed to delete and recreate the remote, but in fact my normal push command worked exactly the same as the clone above, and the remote did not change:

$ git push https://github.com/user-or-organisation/myrepo.git
Username: <my-username>
Password: <my-personal-access-token>

(@YMHuang put me on the right track with the documentation link.)