Document how to avoid the following site build failure

Embedded error: Error rendering Maven report: org.dom4j.DocumentFactory cannot be cast to org.dom4j.DocumentFactory

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1485623 13f79535-47bb-0310-9956-ffa450edef68

Author: sebbASF

pom.xml

@@ -198,6 +198,10 @@ CSV files of various types.
           </tags>
         </configuration>
       </plugin>
+      <!-- 
+          NOTE: this requires Maven 3.0.x; when used with Maven 2.2.1, the following error is seen:
+          Embedded error: Error rendering Maven report: org.dom4j.DocumentFactory cannot be cast to org.dom4j.DocumentFactory
+       -->
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>javancss-maven-plugin</artifactId>