[WordPress] Add comment on the password alert mail

/wp-includes/pluggable.php

function wp_new_user_notification($user_id, $plaintext_pass = '') {
 $user = new WP_User($user_id);

 $user_login = stripslashes($user->user_login);
 $user_email = stripslashes($user->user_email);

 // The blogname option is escaped with esc_html on the way into the database in sanitize_option
 // we want to reverse this for the plain text arena of emails.
 $blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);

 $message  = sprintf(__('New user registration on your site %s:'), $blogname) . "\r\n\r\n";
 $message .= sprintf(__('Username: %s'), $user_login) . "\r\n\r\n";
 $message .= sprintf(__('E-mail: %s'), $user_email) . "\r\n";

 @wp_mail(get_option('admin_email'), sprintf(__('[%s] New User Registration'), $blogname), $message);

 if ( empty($plaintext_pass) )
  return;

 $message  = sprintf(__('Username: %s'), $user_login) . "\r\n";
 $message .= sprintf(__('Password: %s'), $plaintext_pass) . "\r\n";
 $message .= wp_login_url() . "\r\n";
 $message .= "Test test test test test test";

 wp_mail($user_email, sprintf(__('[%s] Your username and password'), $blogname), $message);
}