add kotlin-playground styles to PLATFORM.md (#2081)
add kotlin-playground styles to PLATFORM.md (#2081)


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