add test coverage badge

README.md

@@ -27,7 +27,10 @@
     <img alt="Apache-2.0 License" src="https://img.shields.io/github/license/containrrr/watchtower.svg" />
   </a>
   <a href="https://www.codacy.com/app/simskij/watchtower">
-    <img src="https://api.codacy.com/project/badge/Grade/3a4d0fcfd26d45b09b1d7ea3c8c13744"/>
+    <img alt="Codacy Badge" src="https://api.codacy.com/project/badge/Grade/3a4d0fcfd26d45b09b1d7ea3c8c13744"/>
+  </a>
+  <a href="https://www.codacy.com/app/simskij/watchtower?utm_source=github.com&utm_medium=referral&utm_content=containrrr/watchtower&utm_campaign=Badge_Coverage">
+    <img alt="Codacy Badge" src="https://api.codacy.com/project/badge/Coverage/3a4d0fcfd26d45b09b1d7ea3c8c13744" />
   </a>
 </p>