Update README.md (#127)

Author: etolstoy

README.md

@@ -1,6 +1,7 @@
 # Immutable Collections Library for Kotlin
 
-[![JetBrains incubator project](https://jb.gg/badges/incubator.svg)](https://confluence.jetbrains.com/display/ALL/JetBrains+on+GitHub) 
+[![Kotlin Alpha](https://kotl.in/badges/alpha.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) 
 [![Build status](https://teamcity.jetbrains.com/guestAuth/app/rest/builds/buildType:(id:KotlinTools_KotlinxCollectionsImmutable_Build_All)/statusIcon.svg)](https://teamcity.jetbrains.com/viewType.html?buildTypeId=KotlinTools_KotlinxCollectionsImmutable_Build_All)
 [![Maven Central](https://img.shields.io/maven-central/v/org.jetbrains.kotlinx/kotlinx-collections-immutable.svg?label=Maven%20Central)](https://search.maven.org/search?q=g:%22org.jetbrains.kotlinx%22%20AND%20a:%22kotlinx-collections-immutable%22)