add documentation pages for rules/ and lib/ (#119)

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index e0f2a0a..4ae2edc 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,3 +3,16 @@
 load(":workspace.bzl", "bazel_skylib_workspace")
 
 bazel_skylib_workspace()
+
+# Below this line is for documentation generation only,
+# and should thus not be included by dependencies on
+# bazel-skylib.
+
+load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
+git_repository(
+    name = "io_bazel_skydoc",
+    remote = "https://github.com/bazelbuild/skydoc.git",
+    commit = "ac5c106412697ffb9364864070bac796b9bb63d3", # Feb 27, 2019
+)
+load("@io_bazel_skydoc//skylark:skylark.bzl", "skydoc_repositories")
+skydoc_repositories()