Issue #1679660 by rhm50, valthebald, billk2: Add link to cron tutorial on drupal.org.

core/modules/system/lib/Drupal/system/Form/CronForm.php

@@ -89,6 +89,7 @@ public function buildForm(array $form, array &$form_state) {
     $form['cron']['cron_safe_threshold'] = array(
       '#type' => 'select',
       '#title' => t('Run cron every'),
+      '#description' => t('More information about setting up scheduled tasks can be found by <a href="@url">reading the cron tutorial on drupal.org</a>.', array('@url' => url('http://drupal.org/cron'))),
       '#default_value' => $config->get('threshold.autorun'),
       '#options' => array(0 => t('Never')) + drupal_map_assoc(array(3600, 10800, 21600, 43200, 86400, 604800), 'format_interval'),
     );