Update PlanetScale docs

Author: mnapoli

docs/environment/database-planetscale.mdx

@@ -15,6 +15,8 @@ Amongst other features, it offers the following benefits compared to running a d
 
 One extra feature worth mentioning is [the branching concept](https://planetscale.com/docs/concepts/branching): it enables testing schema changes before deploying them in production without downtime.
 
+[Plans](https://planetscale.com/pricing) start at $5/month for single-node PostgreSQL databases.
+
 ## Getting started
 
 To use PlanetScale with Bref, start [by creating a PlanetScale account](https://planetscale.com/).