Point of pedantry:

  > The ignore file lives in your machine’s home directory in ~/.config/git/ignore. Whatever filenames are added to this file are ignored globally at a machine-level.

The wording here is slightly wrong: ~/.config/git/ignore will ignore files per-user on the machine, not "at a machine level". And it's not "your machine's home directory", it's your user's home directory on that machine. Any other users on the same machine will not see this. Git calls this "global", as in "global for the user".

Git config does also have a --system option which modifies the system-level config file, /etc/gitignore. You could probably ignore stuff at the system/machine level (hint: you don't want to), with this. I'd do something like:

  $ sudo git config --system core.excludesFile /etc/gitignore
  $ sudo touch /etc/gitignore

Note however that user config will override this, so any user who has a core.excludesFile setting will not also look at your system level excludes file. Which is a pretty big caveat.