mention about automatic taxes in readme (#61)

Author: u11d-michal-miler

README.md

@@ -101,6 +101,7 @@ module.exports = defineConfig(
 > - The example above will use `PC040100` for each product. See [Advanced Usage](#advanced-usage) for assigning specific tax codes to individual products
 > - The plugin automatically syncs your Medusa stock locations with Avalara locations on startup for accurate tax calculations. However, since Medusa doesn't emit events for stock location changes, if you create or update a location after startup, you'll need to either restart the app or manually call `POST /admin/avalara-cache/feed` to refresh the cache
 > - The plugin fully supports tax-inclusive pricing and automatically respects the region's tax-inclusive preferences
+> - The region's `Automatic Taxes` configuration is critical for API efficiency. When enabled, Medusa calls the tax provider's `getTaxLines` method multiple times during the checkout flow (on shipping address updates, shipping method selection, etc.), which significantly increases the number of requests to the Avalara API. To optimize performance and reduce API calls, it's recommended to disable automatic taxes and instead manually trigger tax calculation by calling [POST `/store/carts/{id}/taxes`](https://docs.medusajs.com/api/store#carts_postcartsidtaxes) from your storefront when the order is ready for review — typically after the shipping method has been selected.
 
 ### 3. Run Database Migration