Add D1 read replication pricing info (#24776)

Author: vy-ton

src/content/docs/d1/best-practices/read-replication.mdx

@@ -410,6 +410,9 @@ To see the impact of read replication and check the how D1 requests are processe
   - `served_by_primary`
 - The [Cloudflare dashboard](https://dash.cloudflare.com/?to=/:account/workers/d1), where you can view your database metrics breakdown by region that processed D1 requests.
 
+## Pricing
+D1 read replication is built into D1, so you don’t pay extra storage or compute costs for read replicas. You incur the exact same D1 [usage billing](/d1/platform/pricing/#billing-metrics) with or without replicas, based on `rows_read` and `rows_written` by your queries.
+
 ## Known limitations
 
 There are some known limitations for D1 read replication.

src/content/partials/workers/d1-pricing.mdx

@@ -23,3 +23,4 @@ To accurately track your usage, use the [meta object](/d1/worker-api/return-obje
 7. Storage is based on gigabytes stored per month, and is based on the sum of all databases in your account. Tables and indexes both count towards storage consumed.
 8. Free limits reset daily at 00:00 UTC. Monthly included limits reset based on your monthly subscription renewal date, which is determined by the day you first subscribed.
 9. There are no data transfer (egress) or throughput (bandwidth) charges for data accessed from D1.
+10. [Read replication](/d1/best-practices/read-replication/) does not charge extra for read replicas. You incur the same usage billing based on `rows_read` and `rows_written` by your queries.