improved docs regarding the requirement of flex (by Tony Theodore)

doc/index.html

@@ -514,7 +514,7 @@ USE_OSGPLUGIN(<plugin2>)
     </tr>
     <tr>
         <td><a href="http://flex.sourceforge.net/">Flex</a></td>
-        <td></td>
+        <td>≥ 2.5.31</td>
     </tr>
     <tr>
         <td><a href="http://gcc.gnu.org/">GCC</a> (gcc, g++)</td>
@@ -583,8 +583,8 @@ USE_OSGPLUGIN(&lt;plugin2&gt;)
 
     <!-- http://www.freebsd.org/ports/ -->
     <pre>pkg_add -r automake110 autoconf262 bash bison cmake \
-           gmake gsed libtool openssl perl pkg-config \
-           scons unzip wget</pre>
+           flex gmake gsed libtool openssl perl \
+           pkg-config scons unzip wget</pre>
 
     <p>
     On 64-bit FreeBSD,