Added README, a bin/serve example server which can be used locally.

README.md

+package:pub_server
+================
+
+This package provides re-usable code for making a pub repository server. The
+`package:pub_server/shelf_pubserver.dart` library provides a shelf HTTP handler
+which provides the HTTP API used by the pub client. One can use different
+backend implementations by implementing the `PackageRepository` interface of
+the `package:pub_server/repository.dart` library.
+
+Example pub repository server
+-----------------------------------------
+
+An *experimental* pub server based on a file system can be found in
+`bin/server.dart`. It uses a filesystem-based `PackageRepository` for storing
+packages and has a read-only fallback to the real `pub.dartlang.org` site,
+if a package is not available locally. This allows one to use all
+`pub.dartlang.org` packages and have additional ones, on top of the publicly
+available packages, available only locally.
+
+It can be run as follows
+```
+~ $ git clone https://github.com/dart-lang/pub_server.git
+~ $ cd pub_server
+~/pub_server $ pub get
+...
+~/pub_server $ dart example/server.dart -d /tmp/package-db
+Listening on http://localhost:8080
+
+To make the pub client use this repository configure your shell via:
+
+    $ export PUB_HOSTED_URL=http://localhost:8080
+```
+
+Using it for uploading new packages to the locally running server or downloading
+packages locally available or via a fallback to `pub.dartlang.org` is as easy
+as:
+
+```
+~/foobar $ export PUB_HOSTED_URL=http://localhost:8080
+~/foobar $ pub get
+...
+~/foobar $ pub publish
+Publishing x 0.1.0 to http://localhost:8080:
+|-- ...
+'-- pubspec.yaml
+
+Looks great! Are you ready to upload your package (y/n)? y
+Uploading...
+Successfully uploaded package.
+```
+
+The fact that the `pub publish` command requires you to grant it oauth2 access -
+which requires a gmail account - is due to the fact that the `pub publish`
+cannot work without authenticatinon or with another authentication scheme.
+*But the information sent by the pub client is not used for this local server
+at the moment*.
+
+
+NOTE: This is package is an alpha version and is not recommended for production
+use.