Issue #3239759: Remind users to back up their database before starting an update

src/Form/UpdaterForm.php

@@ -257,6 +257,12 @@ class UpdaterForm extends FormBase {
       ],
     ];
 
+    $form['backup'] = [
+      '#prefix' => '<strong>',
+      '#markup' => $this->t('It\'s a good idea to <a href=":url">back up your database</a> before you begin.', [':url' => 'https://www.drupal.org/node/22281#s-backing-up-the-database']),
+      '#suffix' => '</strong>',
+    ];
+
     if ($form_state->getUserInput()) {
       $results = [];
     }