Use rules_pkg to create distributions (#234)

This adds a packaging target to create a Bazel Federation-compliant distribution.

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index b44f210..6cd3456 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -15,12 +15,11 @@
 workspace(name = "rules_python")
 
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
 http_archive(
     name = "bazel_federation",
-    url = "https://github.com/bazelbuild/bazel-federation/archive/4da9b5f83ffae17613fa025a0701fa9db9350d41.zip",
-    sha256 = "5b1cf980e327a8f30fc81c00c04007c543e17c09ed612fb645753936de790ed7",
-    strip_prefix = "bazel-federation-4da9b5f83ffae17613fa025a0701fa9db9350d41",
-    type = "zip",
+    url = "https://github.com/bazelbuild/bazel-federation/releases/download/0.0.1/bazel_federation-0.0.1.tar.gz",
+    sha256 = "506dfbfd74ade486ac077113f48d16835fdf6e343e1d4741552b450cfc2efb53",
 )
 
 load("@bazel_federation//:repositories.bzl", "rules_python_deps")
@@ -29,6 +28,9 @@
 load("@bazel_federation//setup:rules_python.bzl",  "rules_python_setup")
 rules_python_setup(use_pip=True)
 
+# Everything below this line is used only for developing rules_python. Users
+# should not copy it to their WORKSPACE.
+
 load("//:internal_deps.bzl", "rules_python_internal_deps")
 rules_python_internal_deps()