Bootstrap kotlin coding guidelines

kotlin.md

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+# Kotlin coding guidelines
+
+These guidelines apply to all Kotlin code we write, regardless of target platform.
+Android-specific conventions do not belong in this document.
+
+## Coding guidelines
+
+We follow the official [Kotlin coding conventions].
+
+## Linting and formatting
+
+All code is formatted with [ktfmt] using `kotlinLangStyle` and the [editorconfig] in the
+[mullvadvpn-app repository] is a reference configuration. We'll typically use additional
+linters such as [detekt], but that can differ on a project basis.
+
+Also see the [main page] for general file format standards to follow.
+
+## CI
+
+All repositories containing Kotlin should have a CI pipeline that fails on compilation errors,
+formatter diffs, detekt findings, and test failures before code is merged to the main branch.
+
+[Kotlin coding conventions]: https://kotlinlang.org/docs/coding-conventions.html
+[ktfmt]: https://github.com/facebook/ktfmt
+[detekt]: https://detekt.dev/
+[mullvadvpn-app repository]: https://github.com/mullvad/mullvadvpn-app
+[detekt configuration]: https://github.com/mullvad/mullvadvpn-app/blob/main/android/config/detekt.yml
+[editorconfig]: https://github.com/mullvad/mullvadvpn-app/blob/main/android/.editorconfig
+[main page]: ./README.md