DOC-1277 Serverless scale to zero (#277)

* DOC-1277 Serverless scale to zero

* Update modules/billing/pages/billing.adoc

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* add: met when all topics are deleted

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: micheleRP

modules/billing/pages/billing.adoc

@@ -18,6 +18,10 @@ Pricing for Serverless clusters depends on the data in, data out, data stored, p
 
 | Uptime | Tracks the number of hours the instance is running.    
 
+| Uptime | Tracks the number of hours the instance is running. +
+
+*NOTE*: Uptime is not charged if partitions = 0 and storage = 0. This condition is met when all topics are deleted.
+
 | Ingress | Tracks the data written into Redpanda (in GB).
 
 All Kafka protocol requests (_except_ message headers) are counted as ingress as soon as they are read by Redpanda's proxy process.