Update README about develop branch

Also update intro with some more context about new repo.

README.md

@@ -4,12 +4,17 @@
 [![Build Status](https://img.shields.io/travis/awslabs/aws-sdk-go.svg)](https://travis-ci.org/awslabs/aws-sdk-go)
 [![Apache V2 License](http://img.shields.io/badge/license-Apache%20V2-blue.svg)](https://github.com/awslabs/aws-sdk-go/blob/master/LICENSE)
 
-aws-sdk-go is a set of clients for all Amazon Web Services APIs,
-automatically generated from the JSON schemas shipped with
-[botocore](http://github.com/boto/botocore).
+The AWS SDK for Go is a set of clients for all Amazon Web Services APIs
+that initially started as
+[Stripe's aws-go](https://github.com/awslabs/aws-sdk-go/tree/50f5f12927d77de6ec71a7473fe1f1081734d908)
+library, and is currently under development to implement full
+service coverage and other standard AWS SDK features.
 
-It supports all known AWS services, and maps exactly to the documented
-APIs, with some allowances for Go-specific idioms (e.g. `ID` vs. `Id`).
+**Note**: Active development is currently happening in the
+[develop](https://github.com/awslabs/aws-sdk-go/tree/develop) branch.
+See this branch to follow along with API changes and interfaces.
+The `master` branch will continue to maintain the current API of
+Stripe's aws-go library until the develop branch is more stable.
 
 ## Caution