chore: README for google-cloud-spanner-executor module (#2818)

suztomo · web-flow · commit 420dcf4ab724 · 2024-01-26T08:59:22.000-05:00
diff --git a/google-cloud-spanner-executor/README.md b/google-cloud-spanner-executor/README.md
@@ -0,0 +1,4 @@
+This module is for Google-internal use ([details](
+http://go/cloud-spanner-client-testing-design)).
+This is not for customers.
+
