Put a file in the empty jar

Change-Id: I1724c42aa662ddbc1b7dea0f0187bf0295ec6221
diff --git a/tools/build/bazel/empty_jar.bzl b/tools/build/bazel/empty_jar.bzl
index 502c304..b339819 100644
--- a/tools/build/bazel/empty_jar.bzl
+++ b/tools/build/bazel/empty_jar.bzl
@@ -17,7 +17,7 @@
     jar = ctx.outputs.jar
 
     cmd = [
-        "touch %s" % (jar.path),
+        "mkdir readme && touch readme/README && jar cf %s readme/README" % (jar.path),
     ]
 
     ctx.action(