Update README.md

Author: Gsantomaggio

README.md

@@ -1,6 +1,7 @@
 # GO stream client for RabbitMQ streaming queues
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 ![Build](https://github.com/rabbitmq/rabbitmq-stream-go-client/workflows/Build/badge.svg)
+[![codecov](https://codecov.io/gh/rabbitmq/rabbitmq-stream-go-client/branch/main/graph/badge.svg?token=HZD4S71QIM)](https://codecov.io/gh/rabbitmq/rabbitmq-stream-go-client)
 
 Experimental client for [RabbitMQ Stream Queues](https://github.com/rabbitmq/rabbitmq-server/tree/master/deps/rabbitmq_stream)