LRM :: add useravatar and username to the menu

lrm_add_user_avatar_to_menu.php

<?php

// COPY AFTER THIS LINE !!!

add_filter( 'wp_nav_menu_items', 'lrm_your_custom_menu_item', 10, 2 );

function lrm_your_custom_menu_item ( $items, $args ) {  
    // Please, don’t forget to replace the theme_location !
    // if the id of my menu was main-menu, I would write if( $args->theme_location == 'main-menu' ) {
    if( $args->theme_location == 'main-menu' ){
        $current_user = wp_get_current_user();
        if($current_user && !empty($current_user->user_login)) {
            $items .= '<li><a href="javascript:void(0)">'
            . get_avatar( $current_user->ID, 32 )
            . ' '
            . $current_user->user_login
            . '</a></li>';        
        }
    }
    return $items;
}

/*
Optionally you could use:
  $current_user->display_name
  $current_user->first_name
  $current_user->last_name
*/

Hello,

I was not able to find place where to paste this? in which file?