README.md: add codecov badge

README.md

@@ -7,6 +7,7 @@
 [![Download](https://img.shields.io/crates/d/dom_query.svg?style=flat)](https://crates.io/crates/dom_query)
 [![docs.rs docs](https://img.shields.io/badge/docs-latest-blue.svg?style=flat)](https://docs.rs/dom_query)
 [![Build Status](https://github.com/niklak/dom_query/actions/workflows/rust.yml/badge.svg?branch=main)](https://github.com/niklak/dom_query/actions/workflows/rust.yml)
+[![codecov](https://codecov.io/gh/niklak/dom_query/graph/badge.svg?token=CFAVOIE61O)](https://codecov.io/gh/niklak/dom_query)
 
 DOM_QUERY is based on HTML crate html5ever and the CSS selector crate selectors. You can use the jQuery-like syntax to query and manipulate an HTML document quickly. **With its help you can query dom and modify it.**.