ci: ensure existence of lib.zip for releases

ensure existence of the lib.zip file for downstream releases. This is
done by creating a base zip file containing a README and updating it
with mozilla_repos if mozilla_repos is not empty.

scripts/create-licenses.sh

@@ -237,8 +237,12 @@ done >> ${TMP_LICENSE_FILE}
 
 cat ${TMP_LICENSE_FILE} > ${VENDOR_LICENSE_FILE}
 
+# initialize zip file to ensure existence (downstream builds depend on libs.zip)
+README="${KUBE_ROOT}/scripts/docs/create-licenses/README.md"
+zip -q "${ZIP_FILENAME}" "${README}"
+
 # Create a package of Mozilla repository source code (only go code).
-[ -n "$mozilla_repos" ] && zip -qr $ZIP_FILENAME $mozilla_repos -i '*.go'
+[ -n "$mozilla_repos" ] && zip -qur $ZIP_FILENAME $mozilla_repos -i '*.go'
 
 # Cleanup vendor directory
 rm -rf vendor

scripts/docs/create-licenses/README.md

@@ -0,0 +1,5 @@
+# create-licenses
+
+This file is intended to be included with the `libs.zip` file that is
+distributed with each `kpt` release. The `libs.zip` file contains a packaging of
+source files necessary to satisfy the Mozilla license.