You can easily add additional details to your receipt by navigating to the settings page in your account. Once you're on that page, scroll down past the list of plans to find the 'View Billing History' button, right below the saved payment method.
When you click on 'View Billing History' a popup will appear with a list of your previous charges (and the next invoice date/total at the top right corner). From here, click on the 'Receipt Settings' button in the lower left corner.
You'll now see the page that allows you to add any additional information you might need to appear on your billing receipts.