document the filtersfile attribute.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@358829 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTypes/filterset.html

@@ -59,6 +59,12 @@ you should ensure that the set of files being filtered are all text files.
     <td vAlign=top>@</td>
     <td vAlign=top align="center">No</td>
   </tr>
+  <tr>
+    <td vAlign=top>filtersfile</td>
+    <td vAlign=top>Specify a single filtersfile.</td>
+    <td vAlign=top><i>n/a</i></td>
+    <td vAlign=top align="center">No</td>
+  </tr>
   <tr>
     <td vAlign=top>recurse</td>
     <td vAlign=top>Indicates whether the replacement text of tokens