[readme] Mention the composite build against Kotlin in README.md
[readme] Mention the composite build against Kotlin in README.md

wiltonlazary/kotlin-native,wiltonlazary/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,wiltonlazary/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,wiltonlazary/kotlin-native,wiltonlazary/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native