add field settings wp

functions.php

<?php 
add_action( 'admin_init', 'wpse_57647_register_settings' );

/* 
 * Register settings 
 */
function wpse_57647_register_settings() 
{
    register_setting( 
        'general', 
        'html_guidelines_message',
        'esc_html' 
    );
    add_settings_section( 
        'site-guide', 
        'Publishing Guidelines', 
        '__return_false', 
        'general' 
    );
    add_settings_field( 
        'html_guidelines_message', 
        'COVID Text', 
        'wpse_57647_print_text_editor', 
        'general', 
        'site-guide' 
    );
}    

/* 
 * Print settings field content 
 */
function wpse_57647_print_text_editor() 
{
    $the_guides = html_entity_decode( get_option( 'html_guidelines_message' ) );
    echo wp_editor( 
        $the_guides, 
        'sitepublishingguidelines', 
        array( 'textarea_name' => 'html_guidelines_message' ) 
    );
}