be more restrictive on what is in the distribution

rules/BUILD

diff --git a/rules/BUILD b/rules/BUILD
index 2f510f4..387019a 100644
--- a/rules/BUILD
+++ b/rules/BUILD
@@ -35,7 +35,10 @@
 
 filegroup(
     name = "standard_package",
-    srcs = glob(["**"]),
+    srcs = glob([
+        "**/BUILD",
+        "**/*.bzl",
+    ]),
 )
 
 # Do not create a bzl_library(). That would create a dependency loop back