README.md: add badges for CI and code coverage (#4)

Author: joelanford

README.md

@@ -1,3 +1,6 @@
 # operator-lib
 
+[![CI](https://github.com/operator-framework/operator-lib/workflows/CI/badge.svg)](https://github.com/operator-framework/operator-lib/actions?query=workflow%3ACI+branch%3Amain)
+[![Coverage Status](https://coveralls.io/repos/github/operator-framework/operator-lib/badge.svg?branch=main)](https://coveralls.io/github/operator-framework/operator-lib?branch=main)
+
 Helpers for Operator developers.