Update documentation of p2.composite.repository ANT task

to add documentation about the new support for source repositories.

Complements
- eclipse-equinox/p2#875

Author: HannesWell

eclipse.platform.common/bundles/org.eclipse.platform.doc.isv/guide/p2_repositorytasks.htm

@@ -1006,6 +1006,25 @@ <h3 class="c2">p2.composite.repository</h3>
                 repositories</a> above.
               </td>
             </tr>
+            <tr>
+              <td>
+                <tt>destination</tt>
+              </td>
+              <td>
+                The destination repository to modify, defined as outlined <a href="#destination_repositories">above</a>.<br>
+                If it already exists, it is modified in place; otherwise, an initially empty repository is created.
+              </td>
+            </tr>
+            <tr>
+              <td>
+                <tt>source</tt>
+              </td>
+              <td>
+                Optional source repositories, as outlined <a href="#source_repositories">above</a>.<br>
+                If specified, the content of the sources is copied to the destination, before it is modified.
+                This can be used to modify a remote (read-only) repository, by specifying it as the <code>source</code>, writing the result to a local <code>destination</code> repository, and then copying the resulting files to the remote server.
+              </td>
+            </tr>
           </table>
         </td>
       </tr>