add readme badges

Author: oharaandrew314

Readme.md

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+![Test](https://github.com/oharaandrew314/dynamodb-kotlin-module/workflows/Test/badge.svg)
+[![codecov](https://codecov.io/gh/oharaandrew314/dynamodb-kotlin-module/branch/master/graph/badge.svg)](https://codecov.io/gh/oharaandrew314/dynamodb-kotlin-module)
+[![License: Unlicense](https://img.shields.io/badge/license-Unlicense-blue.svg)](http://unlicense.org/)
+
 # DynamoDb Kotlin Module
 
 Kotlin Module for the v2 dynamodb-enhanced SDK.