Add codecov badge to project README (#5)

README.md

@@ -1,4 +1,5 @@
 [![Slack](https://img.shields.io/badge/Slack-%23juul--libraries-ECB22E.svg?logo=data:image/svg+xml;base64,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&labelColor=611f69)](https://kotlinlang.slack.com/messages/juul-libraries/)
+[![codecov](https://codecov.io/gh/JuulLabs/khronicle/graph/badge.svg?token=8MHVBLNXB7)](https://codecov.io/gh/JuulLabs/khronicle)
 
 # Khronicle