Update README.md (#1948)

Author: etolstoy

README.md

@@ -1,6 +1,7 @@
 # Kotlin multiplatform / multi-format reflectionless serialization
 
-[![official JetBrains project](https://jb.gg/badges/official.svg)](https://confluence.jetbrains.com/display/ALL/JetBrains+on+GitHub)
+[![Kotlin Stable](https://kotl.in/badges/stable.svg)](https://kotlinlang.org/docs/components-stability.html)
+[![JetBrains official project](https://jb.gg/badges/official.svg)](https://confluence.jetbrains.com/display/ALL/JetBrains+on+GitHub)
 [![GitHub license](https://img.shields.io/badge/license-Apache%20License%202.0-blue.svg?style=flat)](http://www.apache.org/licenses/LICENSE-2.0)
 [![TeamCity build](https://img.shields.io/teamcity/http/teamcity.jetbrains.com/s/KotlinTools_KotlinxSerialization_Ko.svg)](https://teamcity.jetbrains.com/viewType.html?buildTypeId=KotlinTools_KotlinxSerialization_Ko&guest=1)
 [![Kotlin](https://img.shields.io/badge/kotlin-1.6.10-blue.svg?logo=kotlin)](http://kotlinlang.org)