8161531: Provide a javadoc description for the java.datatransfer module

Reviewed-by: ssadetsky

jdk/src/java.datatransfer/share/classes/module-info.java

@@ -23,6 +23,11 @@
  * questions.
  */
 
+/**
+ * Provides interfaces and classes for transferring data between and
+ * within applications.
+ */
+
 module java.datatransfer {
     exports java.awt.datatransfer;
     exports sun.datatransfer to java.desktop;