Add note about Skylark migration in android_instrumentation_test doc

Closes #5008.

PiperOrigin-RevId: 192629969

site/docs/android-instrumentation-test.md

diff --git a/site/docs/android-instrumentation-test.md b/site/docs/android-instrumentation-test.md
index b331b85..55d8635 100644
--- a/site/docs/android-instrumentation-test.md
+++ b/site/docs/android-instrumentation-test.md
@@ -536,3 +536,7 @@
 - Windows support
 - Improved external dependency management
 - Remote test caching and execution
+
+We are planning to rewrite the Android rules in [Skylark](https://docs.bazel.build/versions/master/skylark/concepts.html).
+The `android_instrumentation_test` rule will be part of the rewrite, however,
+its usage will remain unchanged from the end-user perspective.