Add link to help page for a custom module

help page image

 

 

you can use hook_help hook to add help text in the extend module page

<?php

/**
* Implements hook_help().
*/

function cbase_help($route_name, \Drupal\Core\Routing\RouteMatchInterface $route_match) {

  switch ($route_name) {
    case 'help.page.cbase':
      return t('This is help text for custom module');
  }
}