ENGCOM-5706: Update Magento_Authorizenet ReadMe #24279

Author: sidolov

app/code/Magento/Authorizenet/README.md

@@ -1 +1,42 @@
+# Magento_Authorizenet module
+
 The Magento_Authorizenet module implements the integration with the Authorize.Net payment gateway and makes the latter available as a payment method in Magento.
+
+## Extensibility
+
+Extension developers can interact with the Magento_Authorizenet module. For more information about the Magento extension mechanism, see [Magento plug-ins](https://devdocs.magento.com/guides/v2.3/extension-dev-guide/plugins.html).
+
+[The Magento dependency injection mechanism](https://devdocs.magento.com/guides/v2.3/extension-dev-guide/depend-inj.html) enables you to override the functionality of the Magento_Authorizenet module.
+
+### Events
+
+This module dispatches the following events:
+
+ - `checkout_directpost_placeOrder` event in the `\Magento\Authorizenet\Controller\Directpost\Payment\Place::placeCheckoutOrder()` method. Parameters:
+   - `result` is a data object (`\Magento\Framework\DataObject` class).
+   - `action` is a controller object (`\Magento\Authorizenet\Controller\Directpost\Payment\Place`).
+ 
+ - `order_cancel_after` event in the `\Magento\Authorizenet\Model\Directpost::declineOrder()` method. Parameters:
+   - `order` is an order object (`\Magento\Sales\Model\Order` class).
+   
+
+This module observes the following events:
+
+ - `checkout_submit_all_after` event in the `Magento\Authorizenet\Observer\SaveOrderAfterSubmitObserver` file.
+ - `checkout_directpost_placeOrder` event in the `Magento\Authorizenet\Observer\AddFieldsToResponseObserver` file.
+
+For information about events in Magento 2, see [Events and observers](http://devdocs.magento.com/guides/v2.3/extension-dev-guide/events-and-observers.html#events).
+
+### Layouts
+
+This module introduces the following layouts and layout handles in the `view/adminhtml/layout` directory:
+
+- `adminhtml_authorizenet_directpost_payment_redirect`
+
+This module introduces the following layouts and layout handles in the `view/frontend/layout` directory:
+
+- `authorizenet_directpost_payment_backendresponse`
+- `authorizenet_directpost_payment_redirect`
+- `authorizenet_directpost_payment_response`
+
+For more information about layouts in Magento 2, see the [Layout documentation](https://devdocs.magento.com/guides/v2.3/frontend-dev-guide/layouts/layout-overview.html).