Add test coverage link

Author: mxpv

README.md

@@ -27,7 +27,7 @@ These tools make it easy to compile, analyze, and embed `Luau` scripts directly
 - Native support for refs, functions, tables, and vector types
 - Supports Luau code generation for improved performance on supported platforms
 - Built-in [Luau tools](#-using-luau-tools) (`luau-compile` and `luau-analyze`) provided by the build system
-- Excellent test coverage and API [documentation](https://mxpv.github.io/luaz/#luaz.lua)
+- Excellent [test coverage](https://app.codecov.io/gh/mxpv/luaz) and API [documentation](https://mxpv.github.io/luaz/#luaz.lua)
 
 ## 📚 Documentation