This is direct copy and paste from my functions.php using the prefix rl.
Hope this helps you. You can just do a if current_user_can if you want only admins to see this field and if true run rl_register_settings_area().
/**
* Adds a settings section to general settings in WordPress admin.
* @return null
*/
function rl_register_settings_area() {
add_settings_section( 'rl_settings_section', get_bloginfo( 'name' ) . ' Settings', 'rl_setting_prepended_text', 'general');
add_settings_field( 'rl_setting_address1', 'Address', 'rl_create_settings_field', 'general', 'rl_settings_section' );
register_setting( 'general', 'rl_setting_address1' );
register_setting( 'general', 'rl_setting_address2' );
register_setting( 'general', 'rl_setting_address3' );
register_setting( 'general', 'rl_setting_address4' );
register_setting( 'general', 'rl_setting_address5' );
}
add_action( 'admin_menu', 'rl_register_settings_area' );
function rl_create_settings_field() {
?>
<form>
<input name="rl_setting_address1" type="text" value="<?php echo get_option('rl_setting_address1'); ?>" class="code" /> <br />
<input name="rl_setting_address2" type="text" value="<?php echo get_option('rl_setting_address2'); ?>" class="code" /> <br />
<input name="rl_setting_address3" type="text" value="<?php echo get_option('rl_setting_address3'); ?>" class="code" /> <br />
<input name="rl_setting_address4" type="text" value="<?php echo get_option('rl_setting_address4'); ?>" class="code" /> <br />
<input name="rl_setting_address5" type="text" value="<?php echo get_option('rl_setting_address5'); ?>" class="code" /> <br />
</form>
<?php
}
function rl_setting_prepended_text() {
echo 'Change address of your company';
}