I received this error after downloading the zip file and trying to unzip it.
$ unzip terraform-demo.zip
Archive: terraform-demo.zip
End-of-central-directory signature not found. Either this file is not
a zipfile, or it constitutes one disk of a multi-part archive. In the
latter case the central directory and zipfile comment will be found on
the last disk(s) of this archive.
unzip: cannot find zipfile directory in one of terraform-demo.zip or
terraform-demo.zip.zip, and cannot find terraform-demo.zip.ZIP, period.