adds codecov badge

Author: mohanrajpac

README.md

@@ -3,6 +3,7 @@
 [![PHP lint & test](https://github.com/codebtech/wp-feature-flags/actions/workflows/php.yml/badge.svg)](https://github.com/codebtech/wp-feature-flags/actions/workflows/php.yml)
 [![JS lint & test](https://github.com/codebtech/wp-feature-flags/actions/workflows/js.yml/badge.svg)](https://github.com/codebtech/wp-feature-flags/actions/workflows/js.yml)
 [![E2E Tests](https://github.com/codebtech/wp-feature-flags/actions/workflows/e2e.yml/badge.svg)](https://github.com/codebtech/wp-feature-flags/actions/workflows/e2e.yml)
+[![codecov](https://codecov.io/github/codebtech/wp-feature-flags/graph/badge.svg?token=QNUWGCRJGR)](https://codecov.io/github/codebtech/wp-feature-flags)
 
 WordPress Feature flags plugin allow developers to configure features in plugins/themes behind the feature flags on both the server (PHP) and client (JS/TS) side.