chore: update readme to include latest version (#319)

Author: aajtodd

README.md

@@ -1,10 +1,13 @@
 # AWS SDK for Kotlin
-[![Apache 2 licensed][apache-badge]][apache-url]
+[![Apache 2 licensed][apache-badge]][apache-url] [![Maven][maven-badge]][maven-url]
 
 [apache-badge]: https://img.shields.io/badge/license-APACHE2-blue.svg
 [apache-url]: https://github.com/awslabs/aws-sdk-kotlin/blob/main/LICENSE
 
 
+[maven-badge]: https://img.shields.io/maven-central/v/aws.sdk.kotlin/s3.svg?label=Maven
+[maven-url]: https://search.maven.org/search?q=g:aws.sdk.kotlin
+
 This repo contains the AWS SDK for Kotlin and its [public roadmap](https://github.com/awslabs/aws-sdk-kotlin/projects/2)
 
 **The AWS SDK for Kotlin is currently in alpha and is intended strictly for feedback purposes only. Do not use this SDK for production workloads. Refer to the SDK [stability](docs/stability.md) guidelines**
@@ -141,4 +144,4 @@ Please refer to our [security policy](https://github.com/awslabs/aws-sdk-kotlin/
 The SDK supports the following targets:
 
 * [JVM](docs/targets.md#jvm)
-* [Android](docs/targets.md#android) 
+* [Android](docs/targets.md#android)