Add a note on maven.scm.testmode.

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@379180 13f79535-47bb-0310-9956-ffa450edef68

scm/xdocs/releasing.xml

@@ -51,6 +51,8 @@
           <li>Tag the entire source tree with the new tag name</li>
         </ol>
         <p>
+          (Note that you may preview the changes made to project.xml and changes.xml by setting
+          the <code>maven.scm.testmode</code> property).
           When this operation is over, your source control has the released code tagged and ready to deploy.
         </p>
       </subsection>