Add gpo alias for auto branch tracking on push
Add gpo alias for auto branch tracking on push

This sets tracking on upstream branch at origin to be the default
tracking branch on push.

This circumvents this annoying git message:

```

fatal: The current branch <branch> has no upstream branch.
To push the current branch and set the remote as upstream, use

    git push --set-upstream origin <branch>

```

faun/dotfiles,faun/dotfiles