ZCML File
configure.zcml

<configure
    xmlns="http://namespaces.zope.org/browser"
    >
<viewlet
    class=".browser.AddingInfoViewlet"
    layer="zope.app.boston.boston"
    for="zope.app.container.interfaces.IWriteContainer"
    permission="zope.ManageContent"
    name="addinginfo"
    template="viewlet.pt"
    manager="zope.app.boston.ILeft"
    weight="2"
    />
</configure>