Add a note that this is not supported anymore

[fatih]

I think we should add a note to the README and also prevent people opening PR/Issues anymore. As I know aws-sdk-go is being used now across all projects, so this repo should be marked as obsolete.

[naxhh]

+1 I've started using this one a few weeks ago without noticing the official one.

[wingedrhino]

https://aws.amazon.com/blogs/aws/now-available-version-1-0-of-the-aws-sdk-for-go/ 😄

[andrewsomething]

https://github.com/blog/2460-archiving-repositories

[mitchellh]

Good idea @andrewsomething