Add API reference badge to README.md (#4236)

A bit easier and more convenient to find it quickly

Author: qwwdfsad

Diff for: README.md

@@ -5,6 +5,7 @@
 [![GitHub license](https://img.shields.io/badge/license-Apache%20License%202.0-blue.svg?style=flat)](https://www.apache.org/licenses/LICENSE-2.0)
 [![Download](https://img.shields.io/maven-central/v/org.jetbrains.kotlinx/kotlinx-coroutines-core/1.9.0)](https://central.sonatype.com/artifact/org.jetbrains.kotlinx/kotlinx-coroutines-core/1.9.0)
 [![Kotlin](https://img.shields.io/badge/kotlin-2.0.0-blue.svg?logo=kotlin)](http://kotlinlang.org)
+[![KDoc link](https://img.shields.io/badge/API_reference-KDoc-blue)](https://kotlinlang.org/api/kotlinx.coroutines/)
 [![Slack channel](https://img.shields.io/badge/chat-slack-green.svg?logo=slack)](https://kotlinlang.slack.com/messages/coroutines/)
 
 Library support for Kotlin coroutines with [multiplatform](#multiplatform) support.