Updated README to notify users of Dart SDK version requirements.

README.md

Index: README.md
diff --git a/README.md b/README.md
index 1c8c1672b663fd5f3f177095703ed4d87d812256..346085b8233f290c3e36ca9d4f121bd1006a8100 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,21 @@
-TODO: add README
+Dart Synchronous HTTP Client
+============================
+
+**Important Note:** This package requires the RawSynchronousSocket class to
+work, which should become available in version 1.24 of the Dart SDK. If you
+really want to use this package now, you'll have to build the Dart VM from
+the most up-to-date source hosted in dart-lang/sdk.
+
+A simple Dart HTTP client implemented using RawSynchronousSockets to allow for
+synchronous HTTP requests.
+
+Warning: This library should probably only be used to connect to HTTP servers
+that are hosted on 'localhost'. The operations in this library will block the
+calling thread to wait for a response from the HTTP server. The thread can
+process no other events while waiting for the server to respond. As such, this
+synchronous HTTP client library is not suitable for applications that require
+high performance. Instead, such applications should use libraries built on
+asynchronous I/O, including
+[dart:io](https://api.dartlang.org/stable/1.22.1/dart-io/dart-io-library.html)
+and [package:http](https://pub.dartlang.org/packages/http), for the best
+performance.