Added ant info to Howto build a plugin

<section>
        <title>Make ant available on the command line</title>
        <p>
                The following instructions rely heavily on
                <a href="http://ant.apache.org/">ant</a>
                to automate some steps in the process. Since ant
                is distributed as part of Forrest, all you need to do
                is add the ant executable directory to your system path. They
                are located in the
                <code>tools\ant\bin</code>
                subdirectory of your Forrest directory.
        </p>
        <p>
                Alternatively you can prefix all calls to ant in
                the following instructions with the full path to the ant binary directory.
        </p>
    </section>