update READAME.md (#342)

remove no longer required async section and mention external drivers

Author: jxs

README.md

@@ -95,15 +95,18 @@ By default, refinery runs each migration in a single transaction. Alternatively,
 refinery's design was based on [flyway](https://flywaydb.org/) and so, it shares its earlier [philosophy](https://web.archive.org/web/20191226033347/https://flywaydb.org/documentation/command/undo#important-notes) on undo/rollback migrations. 
 Flyway has since changed it's opinion but refinery hasn't. To undo/rollback a migration, you have to generate a new one and write specifically what you want to undo.
 
-## MSRV
+## Support for Additional Database Drivers
 
-refinery aims to support stable Rust, the previous Rust version, and nightly.
+While initially it seemed beneficial to support as many aditional drivers as possible in this repo, with the current bandwidth available by the maintainers it's preferable to create them and maintain them on external repositories (see [here](https://github.com/rust-db/refinery/pull/264#issuecomment-1419198667) for context).
+
+Notable external database drivers:
+
+- [Klickhouse](https://github.com/Protryon/klickhouse) ([Clickhouse](https://clickhouse.tech/docs/en/) database driver with refinery support)
 
-## Async
 
-Starting with version 0.2 refinery supports [tokio-postgres](https://crates.io/crates/tokio-postgres), [`mysql_async`](https://crates.io/crates/mysql_async)
-and [Tiberius](https://github.com/prisma/tiberius)
-For Rusqlite, the best way to run migrations in an async context is to run them inside tokio's [`spawn_blocking`](https://docs.rs/tokio/1.10.0/tokio/task/fn.spawn_blocking.html) for example.
+## MSRV
+
+refinery aims to support stable Rust, the previous Rust version, and nightly.
 
 ## Contributing