No instructions are given on how to get `gmake`

On https://github.com/OpenIndiana/oi-docs/blob/8b3ec5c604674c91fa50e2a976adaf9f34210391/docs/dev/userland.md?plain=1#L135 it tells the user to run `gmake setup`, but there's no instruction on how to get `gmake` before that point. And if you do `# pkg install gmake`, it chokes. Maybe tell the user to install `gnu-make` first?