Add a minimal WORKSPACE file to the distributon. (#182)

* Add a minimal WORKSPACE file to the distributon.

We extract this from the top level workspace so it is easier to keep in sync.

* add better wording

pkg/WORKSPACE

diff --git a/pkg/WORKSPACE b/pkg/WORKSPACE
index 5f94609..46ac341 100644
--- a/pkg/WORKSPACE
+++ b/pkg/WORKSPACE
@@ -23,6 +23,10 @@
 
 bazel_skylib_workspace()
 
+### INTERNAL ONLY - lines after this are not included in the release packaging.
+#
+# Include dependencies which are only needed for development here.
+
 http_archive(
     name = "bazel_stardoc",
     url = "https://github.com/bazelbuild/stardoc/archive/0.4.0.zip",