DOC-1845 explain multi cc in billing (#465)

* DOC-1845 explain multi cc in billing

* add clarifying sentence

* minor edit

* edit, per Towfiqa

Author: micheleRP

modules/billing/pages/billing.adoc

@@ -6,7 +6,7 @@ Redpanda Cloud uses various metrics to measure the consumption of resources.
 
 * All pricing is set in US dollars (USD). 
 * All billing computations are conducted in Coordinated Universal Time (UTC). Billing accrues at hourly intervals. Any usage that is less than an hour is billed for the full hour. 
-* You can view detailed billing activity for each cluster and edit payment methods on the *Billing* page.
+* The *Billing* page shows detailed billing activity for each cluster and lets you manage payment methods. Redpanda charges the credit card marked as the default. The most recently added credit card becomes the default payment method, unless you select a different one.
 
 NOTE: Pricing information is available on https://www.redpanda.com/price-estimator[redpanda.com^]. For questions about billing, contact [email protected].