This exists in the legacy template:
489ebea77b/build.sh (L13C1-L13C39)
And is also used in many modules, though with
`MODULE_DIRECTORY="${MODULE_DIRECTORY:-"/tmp/modules"}"` to not break
things.
And is documented on the website, because I assumed it existed:
https://blue-build.org/reference/module/#module_directory
I know this probably won't change much, but it's still useful for the
scripts.