Clarify the Weaver documentation

- Explicitly mention that Weaver is for *persistent* storage
- Explicitly mention secure deletion requirement

Change-Id: I3eaf7408570ff20c69a21398e39e16be97d2a917
(cherry picked from commit acd066c61425d6b7f512445c6e2883baa28f381e)
Merged-In: I3eaf7408570ff20c69a21398e39e16be97d2a917
diff --git a/weaver/aidl/android/hardware/weaver/IWeaver.aidl b/weaver/aidl/android/hardware/weaver/IWeaver.aidl
index f51034a..ae816ef 100644
--- a/weaver/aidl/android/hardware/weaver/IWeaver.aidl
+++ b/weaver/aidl/android/hardware/weaver/IWeaver.aidl
@@ -20,8 +20,8 @@
 import android.hardware.weaver.WeaverReadResponse;
 
 /**
- * Weaver provides secure storage of secret values that may only be read if the
- * corresponding key has been presented.
+ * Weaver provides secure persistent storage of secret values that may only be
+ * read if the corresponding key has been presented.
  *
  * The storage must be secure as the device's user authentication and encryption
  * relies on the security of these values. The cardinality of the domains of the
@@ -76,7 +76,8 @@
     WeaverReadResponse read(in int slotId, in byte[] key);
 
     /**
-     * Overwrites the identified slot with the provided key and value.
+     * Overwrites the identified slot with the provided key and value, rendering
+     * the previous contents of the slot permanently unrecoverable.
      *
      * The new values are written regardless of the current state of the slot in
      * order to remain idempotent.