Update README.md

Author: belozierov

README.md

@@ -11,6 +11,7 @@
 
 ![macOS](https://github.com/belozierov/SwiftCoroutine/workflows/macOS/badge.svg?branch=master)
 ![Ubuntu](https://github.com/belozierov/SwiftCoroutine/workflows/Ubuntu/badge.svg?branch=master)
+![codecov](https://codecov.io/gh/belozierov/SwiftCoroutine/branch/master/graph/badge.svg)
 
 Many languages, such as Kotlin, JavaScript, Go, Rust, C++, and others, already have [coroutines](https://en.wikipedia.org/wiki/Coroutine) support that makes the use of asynchronous code easier. 
 This feature is not yet supported in Swift, but this can be improved by a framework without the need to change the language.