add note about billing for transaction-based profiling

Author: vbro

docs/pricing/index.mdx

@@ -86,7 +86,9 @@ Tracing is enabled by and will be billed for in spans.
 
 #### Profiling Pricing
 
-Profile Hours are determined by the length of the profile in milliseconds and are billed in hours. Partial hours are prorated and rounded down to the nearest cent. Profile Hours can only be purchased with your PAYG budget.
+Profile Hours are determined by the length of the profile in milliseconds and are billed in hours. Partial hours are prorated and rounded down to the nearest cent.
+[Transaction-Based profiling](/product/explore/profiling/transaction-vs-continuous-profiling/) is billed based on the size of the profile payload, by comparing with the duration of a continuous profile of a similar size.
+Profile Hours can only be purchased with your PAYG budget.
 
 **Continuous Profile Hours**