add v4-beta tag warning

Author: nicktrn

docs/self-hosting/docker.mdx

@@ -105,6 +105,10 @@ docker compose logs -f webapp
 npx trigger.dev@v4-beta init -p <project-ref> -a http://localhost:8030
 ```
 
+<Warning>
+The commands displayed in the webapp are incorrect while v4 is in beta. You should always use the `v4-beta` tag and not `latest`.
+</Warning>
+
 {/* 7. Bonus: Add traefik as a reverse proxy
 
 ```bash