document "input" property

Author: Cristy

docs/script/escape.php/index.html

@@ -392,7 +392,7 @@ <h2>Long Form Attribute Percent Escapes</h2>
   </tr>
   <tr>
     <td>%[input]</td>
-    <td>&nbsp;</td>
+    <td>the input image filename</td>
   </tr>
   <tr>
     <td>%[interlace]</td>