Document the embedded Jetty server.

Change-Id: Ib0df336c9d0d9184b6872d01e17f2489024571a2
diff --git a/src/main/markdown/makinggwtbetter.md b/src/main/markdown/makinggwtbetter.md
index 8dda9a1..d9a9b77 100644
--- a/src/main/markdown/makinggwtbetter.md
+++ b/src/main/markdown/makinggwtbetter.md
@@ -605,6 +605,14 @@
 
 After that you can go to *target/generated-site* and see the generated site.
 
+You can also launch the embedded Jetty server with
+
+```
+mvn jetty:run
+```
+
+and point your browser to [http://localhost:8080](http://localhost:8080).
+
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