mention plugin type explicitly in doc

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@114472 13f79535-47bb-0310-9956-ffa450edef68

artifact/xdocs/tags.xml

@@ -58,7 +58,7 @@
           <tr>
             <td>type</td>
             <td>The type of the artifact 
-              (like <i>jar</i> or <i>war</i>). Type is used for
+              (like <i>jar</i> or <i>war</i> or <i>plugin</i>). Type is used for
               computing a detination path in repository.            
             </td>
             <td>No</td>