convex-backend PR 82: Update database usage section for self hosted (#36936)

Fixes the database section since convex recently started adding internal data to postgres and MySQL as well in self hosted versions.

[Source](https://github.com/get-convex/convex-backend/tree/main/self-hosted#running-the-database-on-postgres-or-mysql)

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Co-authored-by: baqirkhan <[email protected]>
GitOrigin-RevId: 184765d6efb01b4f32ea4cbcc6c1920a681b8518

Author: 2 people

npm-packages/docs/docs/understanding/index.mdx

@@ -45,8 +45,8 @@ relations, like `tasks` assigned to a `user` using IDs to reference documents in
 other tables.
 
 The Convex cloud offering runs on top of Amazon RDS using MySQL as its
-persistence layer. The Open Source version uses SQLite, and soon Postgres or
-MySQL. The database is ACID-compliant and uses
+persistence layer. The Open Source version uses SQLite, Postgres and MySQL. The
+database is ACID-compliant and uses
 [serializable isolation and optimistic concurrency control](/docs/database/advanced/occ.md).
 All that to say, Convex provides the strictest possible transactional
 guarantees, and you never see inconsistent data.