docs: add code coverage badge back (#255)

Author: linrongbin16

README.md

@@ -5,7 +5,7 @@
 <a href="https://github.com/linrongbin16/commons.nvim"><img alt="commons.nvim" src="https://img.shields.io/badge/power_by-commons.nvim-pink" /></a>
 <a href="https://luarocks.org/modules/linrongbin16/gitlinker.nvim"><img alt="luarocks" src="https://img.shields.io/luarocks/v/linrongbin16/gitlinker.nvim" /></a>
 <a href="https://github.com/linrongbin16/gitlinker.nvim/actions/workflows/ci.yml"><img alt="ci.yml" src="https://img.shields.io/github/actions/workflow/status/linrongbin16/gitlinker.nvim/ci.yml?label=ci" /></a>
-<!-- <a href="https://app.codecov.io/github/linrongbin16/gitlinker.nvim"><img alt="codecov" src="https://img.shields.io/codecov/c/github/linrongbin16/gitlinker.nvim/main?label=codecov" /></a> -->
+<a href="https://app.codecov.io/github/linrongbin16/gitlinker.nvim"><img alt="codecov" src="https://img.shields.io/codecov/c/github/linrongbin16/gitlinker.nvim/main?label=codecov" /></a>
 </p>
 
 > Maintained fork of [ruifm's gitlinker](https://github.com/ruifm/gitlinker.nvim), refactored with bug fixes, ssh host alias, blame support and other improvements.