Add Codecov badge to README

Add a Codecov status badge to the README to display the repository's coverage report. The badge links to the project's Codecov page and uses the for-the-badge style for prominent visibility.

Author: ReenigneArcher

README.md

@@ -1,6 +1,7 @@
 # GameDB
 
 [![GitHub Workflow Status (DB)](https://img.shields.io/github/actions/workflow/status/lizardbyte/gamedb/update-db.yml.svg?branch=master&label=update%20db&logo=github&style=for-the-badge)](https://github.com/LizardByte/GameDB/actions/workflows/update-db.yml?query=branch%3Amaster)
+[![Codecov](https://img.shields.io/codecov/c/gh/LizardByte/GameDB.svg?token=AG91ICECDX&style=for-the-badge&logo=codecov&label=codecov)](https://app.codecov.io/gh/LizardByte/GameDB)
 
 This repository clones IGDB to gh-pages to be consumed by LizardByte projects, such as LizardByte/Sunshine.