/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package hudson.plugins.disk_usage;

import hudson.Extension;
import hudson.model.ManagementLink;
import hudson.model.RootAction;

/**
 *
 * @author Lucie Votypkova
 */
@Extension
public class DiskUsageManagement extends ManagementLink implements RootAction{

   public final String[] COLUMNS = new String[]{"Project name", "Builds", "Workspace", "JobDirectory (without builds)"};

        public String getIconFileName() {
            return "/plugin/disk-usage/icons/diskusage48.png";
        }

        public String getDisplayName() {
            return Messages.DisplayName();
        }

        public String getUrlName() {
            return "plugin/disk-usage/";
        }

        @Override public String getDescription() {
            return Messages.Description();
        }     
    
}

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package hudson.plugins.disk_usage;

import hudson.Extension;
import hudson.model.ManagementLink;
import hudson.model.RootAction;
import java.io.IOException;
import javax.servlet.ServletException;
import jenkins.model.Jenkins;
import org.kohsuke.stapler.StaplerRequest;
import org.kohsuke.stapler.StaplerResponse;

/**
 *
 * @author Lucie Votypkova
 */
@Extension
public class DiskUsageManagement extends ManagementLink implements RootAction{

   public final String[] COLUMNS = new String[]{"Project name", "Builds", "Workspace", "JobDirectory (without builds)"};

        public String getIconFileName() {
            return "/plugin/disk-usage/icons/diskusage48.png";
        }

        public String getDisplayName() {
            return Messages.DisplayName();
        }

        public String getUrlName() {
            return "disk-usage";
        }

        @Override public String getDescription() {
            return Messages.Description();
        }  
        
        public void doIndex(StaplerRequest req, StaplerResponse res) throws ServletException, IOException{
            DiskUsagePlugin plugin = Jenkins.getInstance().getPlugin(DiskUsagePlugin.class);
            res.sendRedirect(Jenkins.getInstance().getRootUrl() + "plugin/disk-usage");
        }
    
}

Fix link in menu on main page.