Update README to point to new source location (#21)

diff --git a/README.md b/README.md
index f1f3bfd..36ab294 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1 @@
-A package that provides a [shelf][] handler for serving a `packages/` directory.
-It's intended to be usable as the first handler in a [`Cascade`][cascade], where
-any requests that include `/packages/` are served package assets, and all other
-requests cascade to additional handlers.
-[shelf]: http://github.com/dart-lang/shelf
-[cascade]: http://www.dartdocs.org/documentation/shelf/latest/index.html#shelf/shelf.Cascade
+This package has moved to https://github.com/dart-lang/shelf/tree/master/pkgs/shelf_packages_handler