doc: add CI badge

Author: jim80net

README.md

@@ -3,6 +3,7 @@
 This AWS Lambda function connects to an AWS Elasticache instance running in redis mode,
 and submits slowlog entry metrics to a Datadog account. 
 
+![Rspec and Release](https://github.com/scribd/elasticache-slowlog-to-datadog/workflows/Rspec%20and%20Release/badge.svg)
 [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release)