docs(docker-compose): clarify tool choice (#13399)

plugins/docker-compose/README.md

@@ -2,6 +2,8 @@
 
 This plugin provides completion for [docker-compose](https://docs.docker.com/compose/) as well as some
 aliases for frequent docker-compose commands.
+This plugin chooses automatically between the legacy `docker-compose` command and the modern 
+`docker compose` subcommand, preferring `docker-compose` when both are available.
 
 To use it, add docker-compose to the plugins array of your zshrc file: