CloneableSmartAsset: clarify the setKey() javadoc (#2018)

Author: stephengold

jme3-core/src/main/java/com/jme3/asset/CloneableSmartAsset.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009-2012 jMonkeyEngine
+ * Copyright (c) 2009-2023 jMonkeyEngine
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -65,13 +65,14 @@ public interface CloneableSmartAsset extends Cloneable {
     public CloneableSmartAsset clone();
 
     /**
-     * Set by the {@link AssetManager} to track this asset. 
+     * Assigns the specified AssetKey to the asset.
      * 
-     * Only clones of the asset has this set, the original copy that
-     * was loaded has this key set to null so that only the clones are tracked
-     * for garbage collection. 
+     * This is invoked by the {@link AssetManager}.
+     * Only clones of the asset have non-null keys. The original copy that
+     * was loaded has no key assigned. Only the clones are tracked
+     * for garbage collection.
      * 
-     * @param key The AssetKey to set
+     * @param key The AssetKey to assign
      */
     public void setKey(AssetKey key);