docs: add code-coverage badge to readme

Jost Voelker · Jost Voelker · commit f81df92d0a03 · 2023-06-29T15:17:08.000+02:00
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 # Installation
 
+[![codecov](https://codecov.io/gh/brainbits/database-command/branch/main/graph/badge.svg?token=DQUKMP6AF5)](https://codecov.io/gh/brainbits/database-command)
+
 Register the commands in your `services.yaml`.
 
 ```yaml
