add DeferredGeneration sample

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1887250 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/examples/src/org/apache/poi/examples/xssf/streaming/DeferredGeneration.java b/src/examples/src/org/apache/poi/examples/xssf/streaming/DeferredGeneration.java
index e3907a9..9c53c4e 100644
--- a/src/examples/src/org/apache/poi/examples/xssf/streaming/DeferredGeneration.java
+++ b/src/examples/src/org/apache/poi/examples/xssf/streaming/DeferredGeneration.java
@@ -25,6 +25,11 @@
 import java.io.FileOutputStream;
 import java.io.IOException;
 
+/**
+ * This sample demonstrates how to use DeferredSXSSFWorkbook to generate workbooks in a streaming way.
+ * This approach avoids the use of temporary files and can be used to output to streams like
+ * HTTP response streams.
+ */
 public class DeferredGeneration {
 
     public static void main(String[] args) throws IOException {