Added the description of boxes_flow.

docs/index.html

@@ -9,7 +9,7 @@
 
 <div align=right class=lastmod>
 <!-- hhmts start -->
-Last Modified: Sun Nov 17 06:32:44 UTC 2013
+Last Modified: Mon Mar 24 10:19:52 UTC 2014
 <!-- hhmts end -->
 </div>
 
@@ -264,6 +264,12 @@ are M = 1.0, L = 0.3, and W = 0.2, respectively.
 <td style="border-top:1px blue solid" align=right>&uarr;</td>
 </tr></table>
 <p>
+<dt> <code>-F <em>boxes_flow</em></code> 
+<dd> Specifies how much a horizontal and vertical position of a text matters
+when determining a text order. The value should be within the range of 
+-1.0 (only horizontal position matters) to +1.0 (only vertical position matters).
+The default value is 0.5.
+<p>
 <dt> <code>-C</code> 
 <dd> Suppress object caching. 
 This will reduce the memory consumption but also slows down the process.