Suggestion to add information about environment

Signed-off-by: Benjamin Balder Bach <[email protected]>

Author: benjaoming

docs/reference/compose_exec.md

@@ -28,3 +28,6 @@ This is the equivalent of `docker exec` targeting a Compose service.
 
 With this subcommand, you can run arbitrary commands in your services. Commands allocate a TTY by default, so
 you can use a command such as `docker compose exec web sh` to get an interactive prompt.
+
+Environment from existing configuration is applied.
+You can for instance introspect your environment by running `docker-compose exec web "/usr/bin/env"`.