Update enterprise_invoices.mdx

make sub heading so it shows in toc on righthand side

Author: LaurenceJJones

crowdsec-docs/unversioned/console/enterprise_plan/enterprise_invoices.mdx

@@ -27,12 +27,12 @@ You will be redirected to the `Manage your plan` page.
 
 At the bottom of the page, you can see the `Invoice history` section. Here you can see all the invoices associated with your organization. Click on the desired invoice adn download it.
 
-# Receiving invoices by email
+## Receiving invoices by email
 
 You can also receive your invoices by email. To do so, go to the `Settings` page and click on the `Notifications`  entry menu. Here, you can configure your email preferences and enable invoice notifications.
 
  ![invoicing settings](/img/console/enterprise_invoices/invoices_invoicing_notification_settings.png)
 
  On the same page, you can also add recipients who will receive the invoices by email. you can add multiple recipients by separating their email addresses with a semicolon `;`.
 
-![invoicing recipients](/img/console/enterprise_invoices/invoices_invoicing_recipients.png)
+![invoicing recipients](/img/console/enterprise_invoices/invoices_invoicing_recipients.png)