docs: update README badges for improved visibility and consistency

Author: durimkryeziu

README.md

@@ -1,9 +1,11 @@
 # Exercises for Programmers -  Java
 
-[![Build](https://img.shields.io/github/actions/workflow/status/durimkryeziu/exercises-for-programmers-java/build.yml?branch=main&logo=github)](https://github.com/durimkryeziu/exercises-for-programmers-java/actions)
-[![License: MIT](https://img.shields.io/github/license/durimkryeziu/exercises-for-programmers-java)](https://github.com/durimkryeziu/exercises-for-programmers-java/blob/main/LICENSE)
-![Java](https://img.shields.io/badge/Java-25-blue?logo=openjdk)
-![Commits](https://img.shields.io/github/commit-activity/t/durimkryeziu/exercises-for-programmers-java?logo=git&color=%23F05032)
+[![Build](https://img.shields.io/github/actions/workflow/status/durimkryeziu/exercises-for-programmers-java/build.yml?branch=main&logo=github&style=flat-square)](https://github.com/durimkryeziu/exercises-for-programmers-java/actions)
+[![Codecov](https://img.shields.io/codecov/c/github/durimkryeziu/exercises-for-programmers-java?style=flat&logo=codecov&color=%23F01F7A)
+](https://app.codecov.io/github/durimkryeziu/exercises-for-programmers-java)
+![Java](https://img.shields.io/badge/Java-25-blue?logo=openjdk&style=flat-square)
+![Commits](https://img.shields.io/github/commit-activity/t/durimkryeziu/exercises-for-programmers-java?logo=git&color=%23F05032&style=flat-square)
+[![License: MIT](https://img.shields.io/github/license/durimkryeziu/exercises-for-programmers-java?style=flat-square)](https://github.com/durimkryeziu/exercises-for-programmers-java/blob/main/LICENSE)
 
 Exercises for Programmers: 57 Challenges to Develop Your Coding Skills by Brian P. Hogan in Java