Update local setup steps of contributing guide

Author: Cosmin Ciobanu

CONTRIBUTING.md

@@ -4,12 +4,14 @@
 
 Ensure you are not running a local postgres server (such as the Postgres app for OSX).
 
-Start up / tear down the local network:
+Start up / tear down the local network & containers:
 
 ```bash
-> ./bin/local up
-> ./bin/local down
+> export SERVER_KEY=$(cat world/server.key)
+> export SERVER_CERT=$(cat world/server.crt)
+> docker-compose up
 ```
+If the above stops working, check the [Github action](https://github.com/typelevel/skunk/blob/main/.github/workflows/ci.yml) for what runs during CI.
 
 Then to run all the tests, in a separate window: