Now that toolforge_i18n is a submodule, the initial setup and updates
need to look a little different. (In practice, I expect I’ll usually
omit the `git submodule update` when I know there weren’t any submodule
changes, but that’s besides the point.) Also refresh the commands
generally to reflect what I usually run these days.

Also fix the path in the setup – I changed the origin URL from
lucaswerkmeister/tool-* to toolforge-repos/* in ec75eef0, but
neglected to update the `cd` command at the same time.