Add README.md

This repository is archived. The development is moved to https://github.com/JetBrains/kotlin.
Issue tracking and discussions are moved too, see #4079.

README.md

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+[![official project](http://jb.gg/badges/official.svg)](https://confluence.jetbrains.com/display/ALL/JetBrains+on+GitHub)
+# Kotlin/Native  #
+
+The development of Kotlin/Native was moved to https://github.com/JetBrains/kotlin.
+Because of that, this repository was archived.
+
+The state of source code prior to the archiving is available in the new default branch,
+[`archive`](https://github.com/JetBrains/kotlin-native).
+
+Instead of creating new issues in this repository or commenting the existing ones,
+please use other ways to communicate: https://github.com/JetBrains/kotlin-native/issues/4079