IWeaver.aidl: document that throttling must be per-slot

Change-Id: Ice26840d22fa55aaa472eec53e6962d6bc8bdd1d
diff --git a/weaver/aidl/android/hardware/weaver/IWeaver.aidl b/weaver/aidl/android/hardware/weaver/IWeaver.aidl
index ae816ef..30168e3 100644
--- a/weaver/aidl/android/hardware/weaver/IWeaver.aidl
+++ b/weaver/aidl/android/hardware/weaver/IWeaver.aidl
@@ -58,7 +58,9 @@
      * Throttling must be used to limit the frequency of failed read attempts.
      * The value is only returned when throttling is not active, even if the
      * correct key is provided. If called when throttling is active, the time
-     * until the next attempt can be made is returned.
+     * until the next attempt can be made is returned. Throttling must be
+     * applied on a per-slot basis so that a successful read from one slot does
+     * not reset the throttling state of any other slot.
      *
      * Service status return:
      *