Update README.md with test status badge (#142)

Author: typotter

README.md

@@ -1,5 +1,5 @@
 # Common library for Eppo's JavasScript SDK
-
+[![Test and lint SDK](https://github.com/Eppo-exp/js-sdk-common/actions/workflows/lint-test-sdk.yml/badge.svg)](https://github.com/Eppo-exp/js-sdk-common/actions/workflows/lint-test-sdk.yml)
 [![](https://img.shields.io/npm/v/@eppo/js-client-sdk-common)](https://www.npmjs.com/package/@eppo/js-client-sdk-common)
 [![](https://img.shields.io/static/v1?label=GitHub+Pages&message=API+reference&color=00add8)](https://eppo-exp.github.io/js-client-sdk/js-client-sdk-common.html)
 [![](https://data.jsdelivr.com/v1/package/npm/@eppo/js-client-sdk-common/badge)](https://www.jsdelivr.com/package/npm/@eppo/js-client-sdk-common)