Readme: Add test coverage badge.
@@ -2,6 +2,8 @@ Linux: [![Linux Build](https://travis-ci.org/FascinatedBox/lily.svg?branch=maste
Windows: [![Windows Build](https://ci.appveyor.com/api/projects/status/github/FascinatedBox/lily?svg=true)](https://ci.appveyor.com/project/FascinatedBox/lily)
+Test Coverage: [![codecov](https://codecov.io/gh/FascinatedBox/lily/branch/master/graph/badge.svg)](https://codecov.io/gh/FascinatedBox/lily)
+
## Lily
Lily is a programming language focused on expressiveness and type safety.
