clarify further since it required one more hop on confirmation

Author: HeartSaVioR

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateStore.scala

@@ -673,7 +673,10 @@ case class RangeKeyScanStateEncoderSpec(
   }
 }
 
-/** The encoder specification for [[TimestampAsPrefixKeyStateEncoder]]. */
+/**
+ * The encoder specification for [[TimestampAsPrefixKeyStateEncoder]].
+ * The encoder expects the provided key schema to have [original key fields..., timestamp field].
+ */
 case class TimestampAsPrefixKeyStateEncoderSpec(keySchema: StructType)
   extends KeyStateEncoderSpec {
 
@@ -688,7 +691,10 @@ case class TimestampAsPrefixKeyStateEncoderSpec(keySchema: StructType)
   }
 }
 
-/** The encoder specification for [[TimestampAsPostfixKeyStateEncoder]]. */
+/**
+ * The encoder specification for [[TimestampAsPostfixKeyStateEncoder]].
+ * The encoder expects the provided key schema to have [original key fields..., timestamp field].
+ */
 case class TimestampAsPostfixKeyStateEncoderSpec(keySchema: StructType)
   extends KeyStateEncoderSpec {