BELOW THIS LINE:

/* preview logo */
    options::$fields['general']['tracking_code']        = array('type' => 'st--textarea' , 'label' => __( 'Tracking Code' , 'cosmotheme' ) , 'hint' => __( 'Paste your Google Analytics or other tracking code here,<br /> and it will be added into the footer of your template.' , 'cosmotheme' ) );


ADD THIS LINE:

    /*footer text */
    options::$fields['general']['footer_text']        = array('type' => 'st--textarea' , 'label' => __( 'Footer copyright text' , 'cosmotheme' ));