Add s3proxydocker to references

Fixes #103.

README.md

@@ -94,6 +94,7 @@ References
 * [fake-s3](https://github.com/jubos/fake-s3) and [S3 ninja](https://github.com/scireum/s3ninja) provide functionality similar to S3Proxy when using the filesystem provider
 * Another project named [s3proxy](https://github.com/abustany/s3proxy) provides HTTP access to non-S3-aware applications
 * [GlacierProxy](https://github.com/bouncestorage/glacier-proxy) and [SwiftProxy](https://github.com/bouncestorage/swiftproxy) provide similar functionality for the Amazon Glacier and OpenStack Swift APIs
+* [s3proxydocker](https://github.com/ritazh/s3proxydocker) packages S3Proxy as a Docker container
 * [swift3](https://github.com/openstack/swift3) provides an S3 middleware for OpenStack Swift
 
 License