update Readme

Author: kwstannard

Readme.md

@@ -108,27 +108,9 @@ Note that you may need to run `spring stop` first.
 
 # Developing and Testing
 
-This repo uses [Roadshow] to generate a [Docker Compose] file for each
-supported version of Rails (with a compatible version of Ruby for each one).
+Requirements: docker or podman with docker compatibility layer.
 
-To run specs across all versions, you can either [get the Roadshow tool] and
-run `roadshow run`, or use Docker Compose directly:
-
-```
-$ for fn in scenarios/*.docker-compose.yml; do docker-compose -f $fn run --rm scenario; done
-```
-
-You can also manually run the Rails console and server on each version with
-`roadshow run rake console` and `roadshow run rake server`, or run them on a
-specific version with, e.g., `roadshow run -s rails40 rake console`.
-
-To update the set of scenarios, edit `scenarios.yml` and run `roadshow
-generate`, although the Gemfiles in the `scenarios` directory need to be
-maintained manually.
-
-[Roadshow]: https://github.com/rf-/roadshow
-[Docker Compose]: https://docs.docker.com/compose/
-[get the Roadshow tool]: https://github.com/rf-/roadshow/releases
+To run the test suite against supported Ruby and Rails versions, run `bin/test`.
 
 # Alternative