ICU-23055 Add warning about our plan to remove in locale-service-provider.md

docs/userguide/icu4j/locale-service-provider.md

diff --git a/docs/userguide/icu4j/locale-service-provider.md b/docs/userguide/icu4j/locale-service-provider.md
index 480ba85..e836b06 100644
--- a/docs/userguide/icu4j/locale-service-provider.md
+++ b/docs/userguide/icu4j/locale-service-provider.md
@@ -20,6 +20,8 @@
 
 ---
 
+# WARNING: Please note that for ICU 78 (2025-oct) we are planning to remove the ICU4J Locale Service Provider. See the [ICU 77 page](https://unicode-org.github.io/icu/download/77.html) for details.
+
 ## Overview
 
 Java SE 6 introduced a new feature which allows Java user code to extend locale