make sure the packaging metadata is not lost;

this should be automated by zpkg, but just name it specifically for now

src/ZConfig/PACKAGE.cfg

@@ -17,6 +17,9 @@
   # Python modules from the package:
   *.py
 
+  # Packaging metadata must be included as it will be used to build/install:
+  *.cfg
+
   # Child packages:
   components
   tests