Add snippet for adding content above the login/register form (#39177)

docs/snippets/before-login--register-form.md

@@ -0,0 +1,35 @@
+# Add a message above the login / register form
+
+> This is a **Developer level** doc. If you are unfamiliar with code and resolving potential conflicts, select a [WooExpert or Developer](https://woocommerce.com/customizations/) for assistance. We are unable to provide support for customizations under our  [Support Policy](http://www.woocommerce.com/support-policy/?_gl=1*1lw1nc0*_gcl_au*MTUzMTUyODE0MS4xNjg0NTA1MDgy*_ga*NzE5NDY2OTA4LjE2NjA3MzY5NDM.*_ga_98K30SHWB2*MTY4OTAwODAwNy4xNDYuMC4xNjg5MDA4MDA3LjAuMC4w&_ga=2.99723742.1943287701.1688936513-719466908.1660736943).
+
+This code will add a custom message above the login/register form on the user’s my-account page.
+
+```php
+if ( ! function_exists( 'YOUR_PREFIX_login_message' ) ) {
+    /**
+     * Add a message above the login / register form on my-account page
+     */
+    function YOUR_PREFIX_login_message() {
+        if ( get_option( 'woocommerce_enable_myaccount_registration' ) == 'yes' ) {
+            ?>
+            <div class="woocommerce-info">
+            <p><?php _e( 'Returning customers login. New users register for next time so you can:', 'YOUR-TEXTDOMAIN' ); ?></p>
+            <ul>
+                <li><?php _e( 'View your order history', 'YOUR-TEXTDOMAIN' ); ?></li>
+                <li><?php _e( 'Check on your orders', 'YOUR-TEXTDOMAIN' ); ?></li>
+                <li><?php _e( 'Edit your addresses', 'YOUR-TEXTDOMAIN' ); ?></li>
+                <li><?php _e( 'Change your password', 'YOUR-TEXTDOMAIN' ); ?></li>
+            </ul>
+            </div>
+            <?php
+        }
+    }
+    add_action( 'woocommerce_before_customer_login_form', 'YOUR_PREFIX_login_message' );
+}
+```
+
+Please note that for this code to work, the following options must be checked in the WooCommerce “Accounts & Privacy” settings:
+
+- Allow customers to create an account during checkout
+- Allow customers to create an account on the "My Account" page
+