8161407: Provide a javadoc description for java.desktop module

Reviewed-by: bpb
diff --git a/jdk/src/java.desktop/share/classes/module-info.java b/jdk/src/java.desktop/share/classes/module-info.java
index 77150e1..504c0c2 100644
--- a/jdk/src/java.desktop/share/classes/module-info.java
+++ b/jdk/src/java.desktop/share/classes/module-info.java
@@ -23,6 +23,10 @@
  * questions.
  */
 
+/**
+  * java.desktop defines and exports the user interface, graphics
+  * and imaging APIs of the Java SE platform.
+  */
 module java.desktop {
     requires public java.datatransfer;
     requires public java.xml;