How to and a extra meta box to custom post type in wordpress

I'm trying to create a slider for my wordpress theme. The image, title, and content are OK, but I want to show also a "read more" link, but I cannot add extra meta boxes to my current code.Could anybody help me please. I'm trying:

/* Sliders Custom Post */
    register_post_type( 'slider', /* this can be seen at the URL as a parameter and a unique id for the custom post */
        array(
            'labels' => array(
                'name' => __( 'Slider','Slider' ), /* The Label of the custom post */
                'singular_name' => __( "Sliders", 'textdomain_topbest' ) /* The Label of the custom post */

            ),
            'public' => true,
            'has_archive' => true,
            'rewrite' => array('slug' => 'slider'), /* The slug of the custom post */
            'supports' => array( 'title', 'editor', 'thumbnail' ), /* enable basic for text editing */
        )
    );

PHP:

 

You need some tweak and hack the code to get what you want.. just analysis the code existing there... and think with logic programming algorithm and try tom move, add or edit the code so the result meet with what you want. some code and call function in wordpress can be found in codex.wordpress.org

 

This is another's guy function. This function adds a custom meta box under post content,but i could not replace it with mine

<?php
add_action( 'after_setup_theme', 'blm_theme_setup' );
function blm_theme_setup() {

    global $content_width;
    /* Set the $content_width for things such as video embeds. */
    if ( !isset( $content_width ) )
    $content_width = 640;

    /* Add theme support for automatic feed links. */
    add_theme_support( 'automatic-feed-links' );

    /* Add theme support for post thumbnails (featured images). */
    add_theme_support( 'post-thumbnails');
}

/* Add your nav menus function to the 'init' action hook. */
add_action( 'init', 'blm_register_menus' );

/* Add custom actions. */
add_action( 'widgets_init', 'blm_register_sidebars' );

// Add menu features
function blm_register_menus() {
    register_nav_menus(array('primary'=>__('Primary Menu'),));
}

function blm_register_sidebars() {
    register_sidebar(
        array(
            'id' => 'primary',
            'name' => __( 'Primary Sidebar', 'blm_basic' ),
            'description' => __( 'The following widgets will appear in the main sidebar div.', 'blm_basic' ),
            'before_widget' => '<aside id="%1$s" class="widget %2$s">',
            'after_widget' => '</aside>',
            'before_title' => '<h4>',
            'after_title' => '</h4>'
        )
    );
}

function blm_init_method() {

    wp_enqueue_script('jquery');
    wp_enqueue_script( 'slides', get_template_directory_uri().'/js/slides.min.jquery.js', array( 'jquery' ) );
   
    }
add_action('wp_enqueue_scripts', 'blm_init_method');

// remove junk from head
remove_action('wp_head', 'rsd_link');
remove_action('wp_head', 'wp_generator');
remove_action('wp_head', 'wlwmanifest_link');
remove_action('wp_head', 'feed_links_extra', 3);
remove_action('wp_head', 'start_post_rel_link', 10, 0);
remove_action('wp_head', 'parent_post_rel_link', 10, 0);
remove_action('wp_head', 'adjacent_posts_rel_link', 10, 0);   


// Custom Post types for Feature project on home page
       add_action('init', 'create_feature');
         function create_feature() {
           $feature_args = array(
              'labels' => array(
               'name' => __( 'Feature Project' ),
               'singular_name' => __( 'Feature Project' ),
               'add_new' => __( 'Add New Feature Project' ),
               'add_new_item' => __( 'Add New Feature Project' ),
               'edit_item' => __( 'Edit Feature Project' ),
               'new_item' => __( 'Add New Feature Project' ),
               'view_item' => __( 'View Feature Project' ),
               'search_items' => __( 'Search Feature Project' ),
               'not_found' => __( 'No feature project found' ),
               'not_found_in_trash' => __( 'No feature project found in trash' )
             ),
           'public' => true,
           'show_ui' => true,
           'capability_type' => 'post',
           'hierarchical' => false,
           'rewrite' => true,
           'menu_position' => 20,
           'supports' => array('title', 'editor', 'thumbnail')
         );
      register_post_type('slider',$feature_args);
    }
    add_filter("manage_feature_edit_columns", "feature_edit_columns");

    function feature_edit_columns($feature_columns){
       $feature_columns = array(
          "cb" => "<input type=\"checkbox\" />",
          "title" => "Title",
       );
      return $feature_columns;
    }
   
   
    //Add Meta Boxes
    //http://wp.tutsplus.com/tutorials/plugins/how-to-create-custom-wordpress-writemeta-boxes/

    add_action( 'add_meta_boxes', 'cd_meta_box_add' );
    function cd_meta_box_add()
    {
        add_meta_box( 'my-meta-box-id', 'Link to Project', 'cd_meta_box_cb', 'feature', 'normal', 'high' );
    }

    function cd_meta_box_cb( $post )
    {
        $url = get_post_meta($post->ID, 'url', true);
        wp_nonce_field( 'my_meta_box_nonce', 'meta_box_nonce' ); ?>

        <p>
            <label for="url">Project url</label>
            <input type="text" name="url" id="url" value="<?php echo $url; ?>" style="width:350px" />
        </p>

        <?php   
    }
   
    add_action( 'save_post', 'cd_meta_box_save' );
    function cd_meta_box_save( $post_id )
    {
        // Bail if we're doing an auto save
        if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;

        // if our nonce isn't there, or we can't verify it, bail
        if( !isset( $_POST['meta_box_nonce'] ) || !wp_verify_nonce( $_POST['meta_box_nonce'], 'my_meta_box_nonce' ) ) return;

        // if our current user can't edit this post, bail
        if( !current_user_can( 'edit_post' ) ) return;

        // now we can actually save the data
        $allowed = array(
            'a' => array( // on allow a tags
                'href' => array() // and those anchors can only have href attribute
            )
        );

        // Probably a good idea to make sure your data is set
        if( isset( $_POST['url'] ) )
            update_post_meta( $post_id, 'url', wp_kses( $_POST['url'], $allowed ) );
    }
?>

Code (markup):

 

The problem is solved thanks forum users.